trans-spliceosomal U6 RNAs of Crithidia fasciculata and Leptomonas seymouri: deviation from the conserved ACAGAG sequence and potential base pairing with spliced leader RNA.

Xu, Guoliang; Wieland, Björn; Bindereif, Albrecht

doi:10.1128/mcb.14.7.4565

Cited by 28 publications

(13 citation statements)

References 52 publications

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“…U6 snRNA gene is present in a single copy (Fig. 4, panel D), as similarly shown for T. brucei (Mottram et al 1989), L. seymouri (Xu et al 1994), L. collosoma (Goldring & Michaeli 1995), Phytomonas sp. and Leishmania mexicana (Wieland & Bindereif 1995).…”

Section: T Cruzi X H Sapiens Snrnas -A Comparison Betweensupporting

confidence: 76%

See 1 more Smart Citation

Cloning and molecular characterization of Trypanosoma cruzi U2, U4, U5, and U6 small nuclear RNAs

Ambrósio

Silva

Cicarelli

2007

Mem. Inst. Oswaldo Cruz

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Small nuclear RNAs (snRNAs) Key words: Trypanosoma cruzi -ribonucleoprotein -small nuclear RNP -small nuclear RNA -spliceosome -trans-splicing In trypanosomes, all mRNAs are processed by transsplicing, in which a common spliced leader sequence (SL) is acquired at the 5'-end to yield mature transcripts (Agabian 1990). SL trans-splicing has been characterized mainly in the trypanosomes and nematodes and requires, in addition to the SL RNP, small nuclear ribonucleoproteins (U snRNPs) U2, U4/U6, and U5 (Tschudi & Ullu 1990). Recently, intervening sequences were described in the PAP gene of Trypanosoma brucei and T. cruzi and a U1 snRNA sequence was described in T. brucei, demonstrating that both cis and trans-splicing can occur in these organisms, with a prevalence of trans (Schnare & Gray 1999, Mair et al. 2000. Hannon et al. (1992) showed that the U1 snRNP is not essential for trans-splicing, but only cis-splicing, as in nematodes.The ribonucleoproteins are complexes that consist of small uridine-rich RNAs (UsnRNAs), interacting with common and specific proteins for each snRNP. In addition these small RNAs possess a uridine-rich Sm site for protein binding, composed of two conserved regions named Sm1 and Sm2, separated by a non-conserved region (Hermann et al. 1995, Séraphin 1995. Seven common proteins of T. brucei snRNP (Sm proteins) have been identified. These include: Sm B, -D1, -D2, -D3, -E, -F, and -G (Palfi et al. 2000). In most eukaryotic organisms, all snRNAs genes are transcribed by RNA polymerase II to produce primary transcripts with a 7-methylguanosine (m 7 G) cap at their 5' end and short extensions at the 3' end. The precursors are exported from the nucleus to the cytoplasm where they assemble into a stable core ribonucleoprotein particle (RNP) through binding to common proteins and the m 7 G cap is hypermethylated to 2,2,7-trimethylguanosine (m 3 G or TMG), as essential maturation step. The complex, consisting of the m 3 G cap and the common proteins, signals reimportation (nuclear reimport) of uridine-rich snRNPs (U snRNPs) into the nucleus (Günzl et al. 2000). The exception is U6 snRNA, which is synthesized by RNA polymerase III and acquires a γ-Me cap (Baserga & Steitz 1993). In trypanosomatids, the U snRNAs are transcribed by RNA polymerase II and they receive an m 3 G cap at the 5' end, except U6 snRNA. The 5' cap protects mRNAs from 5' exoribonucleases and also has an important role in mRNA translation and processing and therefore in the splicing process (O'Mullane & Eperon 1998, Marchetti et al. 1998, Lodish et al. 2000. All U snRNA gene transcription depends on the class 2 promoter (box A and box B elements) of an upstream tRNA gene that is oriented in opposite direction, as observed for T. brucei U2 and U6 snRNAs (Nakaar et al. 1994, Gunzl et al. 1995, Tschudi & Ullu 2002.In this context we proposed the molecular characterization of the T. cruzi snRNAs (U2, U4, U5, and U6) by polymerase chain reaction (PCR) and reverse transcription-PCR. The corresponding amplified sequences were clone...

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Section: T Cruzi X H Sapiens Snrnas -A Comparison Betweensupporting

confidence: 76%

“…3b, indicated by boxes). The single loop of T. cruzi U5 snRNA is conserved among the other trypanosomatids, but L. collosoma (Xu et al 1994), C. fasciculata (Schnare & Gray 2000) and H. sapiens (Baserga & Steitz 1993) show an additional loop at the 3' end.…”

Section: Pcr Amplification Cloning and Sequencing Of T Cruzi U2 U4mentioning

confidence: 99%

Cloning and molecular characterization of Trypanosoma cruzi U2, U4, U5, and U6 small nuclear RNAs

Ambrósio

Silva

Cicarelli

2007

Mem. Inst. Oswaldo Cruz

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“…Interestingly, Crithidia U6 carries a C-to-U change in the second position of the ACAGAG sequence and a compensatory base change of the corresponding SL RNA at position ϩ5 (105). These phylogenetic data also support the 5Ј splice site-U6 interaction.…”

Section: Sl-snrna Interactionssupporting

confidence: 60%

“…Because of space limitation, we chose to discuss snRNAs that have unique features in trypanosomes. Detailed information on U6 and U4 from different trypanosomatid species is not covered in this review but can be found in (8,26,44,105).…”

Section: Snrnas Involved In Trans and Cis Splicingmentioning

confidence: 99%

trans and cis Splicing in Trypanosomatids: Mechanism, Factors, and Regulation

et al. 2003

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mRNA maturation in trypanosomes differs from the process in most eukaryotes mainly because protein-coding genes are transcribed into polycistronic RNAs in this organism (78). Studies from the ongoing genome project suggest that the entire chromosome may be transcribed as large transcripts, but thus far there is no evidence to support the existence of conventional polymerase II promoters (62). The process of trans splicing was discovered 20 years ago when it was found that the different variant surface glycoprotein mRNAs in Trypanosoma brucei carry a common 39-nucleotide (nt) sequence, namely, the spliced leader (SL) sequence (9). It was later established that all trypanosome mRNAs undergo trans splicing (2). The source of the SL sequence was found to be a small capped RNA, the SL RNA (14, 58). Thus, the SL addition serves two purposes: it functions together with polyadenylation in dissecting the polycistronic transcripts, and it provides the cap to mRNAs (2). trans splicing proceeds through a two-step transesterification reaction, analogous to cis splicing but forming a Y structure instead of a lariat intermediate (illustrated in Fig. 1A) (61,88). Although first discovered in trypanosomes, the process was later found in nematodes (41), euglenoids (91), trematodes (73), and recently in chordates (97). Surprisingly, after almost a decade of searching for cis splicing, a single gene carrying a cis-spliced intron was discovered, suggesting that these two splicing processes coexist in trypanosomes, as in all other organisms capable of trans splicing (51).In the last decade, studies have focused on elucidating the mechanism and machinery of pre-mRNA processing in these organisms. The major findings included (i) the identification of the first cis-spliced intron and U1 snRNA that may function exclusively in this process, (ii) the finding and unraveling the function of U5 and SLA1, and (iii) the existence of coupling between trans splicing and polyadenylation. In this review we summarize studies performed mainly in vivo to elucidate structure-function aspects of the SL RNA and the snRNAs with which it interacts. The unique modifications on the SL RNA, including capping and pseudouridylation and their role in SL RNA function and biogenesis, are described. The regulation of splicing and its linkage to polyadenylation is discussed, and data are provided for the existence of splicing factors whose function is well characterized in other eukaryotes. STRUCTURE-FUNCTION ANALYSIS OF THE SL RNAIn the absence of an in vitro system for trans splicing, most of the structure-function studies were performed in vivo in Leptomonas seymouri, Leptomonas collosoma, and Leishmania tarentolae by using tagged SL RNAs (49,53,85,86,108). For some unknown reason, this approach does not work for T. brucei (Elisabetta Ullu, unpublished data). The SL RNA secondary structure of all organisms carrying out trans splicing is similar; it is composed of three stem-loops. In trypanosomatids, The SL sequence is 39 to 41 nt, followed by an intron of varia...

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“…Likewise, no Ul homolog has been identified in trypanosomatids, in which all mRNAs are believed to arise via trans-splicing (for review, see Nilsen 1992). The recent analysis of a new trans-spliceosomal U6 RNA gene (Xu et al 1994) has revealed compensatory base changes within the conserved hexanucleotide sequence of U6 and the 5' splice sites of SL RNAs, suggesting that the 5' splice site-U6 snRNA interaction is universal among splicing systems. In contrast, functions attrib uted to Ul snRNA appear to be dispensable for group II intron removal and for trans-splicing.…”

Section: Functions and Evolution Of The Ul Snrnamentioning

confidence: 99%

SR proteins can compensate for the loss of U1 snRNP functions in vitro.

Tarn¹,

Steitz²

1994

Genes Dev.

147

120

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SR proteins are essential splicing factors that also influence 5' splice site choice. We show that addition of excess mixed SR proteins to a HeLa in vitro splicing system stimulates utilization of a novel 5' splice site (site 125) within the intron of the standard adenovirus pre-mRNA substrate. When Ul snRNPs are debilitated by sequestering the 5' end of Ul snRNA with a 2'-0-methyl oligoribonucleotide, excess SR proteins not only rescue splicing at the normal site and site 125 but also activate yet another 5' splice site (site 47) in the adenovirus intron. One SR protein, SC35, is sufficient to exhibit the above activities. The possibility that excess SR proteins recruit residual unblocked Ul snRNPs to participate in 5' splice site recognition has been ruled out by psoralen cross-linking studies, which demonstrate that the 2'-0-methyl oligoribonucleotide effectively blocks 5' splice site/Ul interaction. Native gel analysis reveals a nearly normal splicing complex profile in the 2'-0-methyl oligoribonucleotide pretreated, SR protein-supplemented extract. These results indicate that SR proteins can replace some functions of the Ul snRNP but underscore the contribution of Ul to the fidelity of 5' splice site selection.[Key Words: SR proteins; Ul snRNPs; pre-mRNA splicing; 5' splice site selection]

show abstract

trans-spliceosomal U6 RNAs of Crithidia fasciculata and Leptomonas seymouri: deviation from the conserved ACAGAG sequence and potential base pairing with spliced leader RNA.

Cited by 28 publications

References 52 publications

Cloning and molecular characterization of Trypanosoma cruzi U2, U4, U5, and U6 small nuclear RNAs

Cloning and molecular characterization of Trypanosoma cruzi U2, U4, U5, and U6 small nuclear RNAs

trans and cis Splicing in Trypanosomatids: Mechanism, Factors, and Regulation

SR proteins can compensate for the loss of U1 snRNP functions in vitro.

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