The alternative splicing factor PSI regulates P-element third intron splicing in vivo.

Abstract

Splicing of the Drosophila P-element third intron (IVS3) is inhibited in somatic cells, restricting transposase expression to the germ line. Somatic inhibition of IVS3 splicing involves the assembly of a multiprotein complex on a regulatory sequence in the IVS3 5' exon. The P-element somatic inhibitor protein (PSI) is a component of this ribonucleoprotein complex and is required for inhibition of IVS3 splicing in vitro. The soma-specific expression pattern of PSI suggests that its low abundance in the germ line allows IVS3 splicing. We demonstrate that ectopic expression of PSI in the female germ line is sufficient to repress splicing of an IVS3 reporter transgene. We also show that IVS3 splicing is activated in somatic embryonic cells in the presence of an antisense PSI ribozyme. These results support the model that PSI is a tissue-specific regulator of IVS3 splicing in vivo.

Drosophila IRBP bZIP heterodimer binds P-element DNA and affects hybrid dysgenesis

“…melanogaster uses multiple endogenous mechanisms to limit P-element transposition. Expression of catalytically active transposase is restricted to the germline by tissue-specific premRNA splicing regulation (41,42). The germline piwi-interacting RNA pathway has been demonstrated to repress transposition in trans and plays a critical role in host adaptation to newly invaded P elements (4,(43)(44)(45).…”

Conservation of functional domains involved in RNA binding and protein–protein interactions in human and Saccharomyces cerevisiae pre-mRNA splicing factor SF1

“…The RNA-binding domain of hSF1 is located between amino acids 94 and 278+ This region includes the maxi-KH domain, which was first described in the hnRNP K protein (Siomi et al+, 1993a) and has been found since in a large number of proteins that function in association with RNA (for references, see Musco et al+, 1996)+ A well-studied example is the product of the FMR1 gene, which is responsible for the fragile X syndrome, a common form of heritable mental retardation in human males (Oostra & Verkerk, 1992;Ashley et al+, 1993;Siomi et al+, 1993b)+ Among the splicing factors, mammalian KSRP (Min et al+, 1997), Drosophila PSI (Siebel et al+, 1995;Adams et al+, 1997) and S. cerevisiae Mer1p (Nandabalan et al+, 1993;Nandabalan & Roeder, 1995) contain one or more KH domains+ These proteins act to promote or repress specific alternative splicing events by interaction with their target pre-mRNA sequences+ It has not been reported whether the KH domain(s) in these proteins are required for activity+…”

High-affinity hnRNP A1 binding sites and duplex-forming inverted repeats have similar effects on 5??? splice site selection in support of a common looping out and repression mechanism

“…The fidelity of pre-messenger RNA splicing relies upon the appropriate selection of specific splicing partners amid a pool of sequences that resemble splice sites+ The process of splice site recognition and pairing, however, has to remain sufficiently flexible to accommodate the generation of alternatively spliced variants+ The control of splice site utilization can operate during the step-wise process of spliceosome assembly, and each step, in principle, can serve as a regulatory point+ Although recent progress has led to the identification of factors that either promote or inhibit the use of a splice site, their mechanisms of action remain poorly understood+ In one of the best-documented cases, the assembly of a soma-specific complex containing PSI, hrp48, and U1 snRNP prevents the binding of U1 snRNP to the authentic 59 splice site in the transposase premRNA of the P-element in Drosophila (Adams et al+, 1997)+ In contrast, the binding of TIA-1 to intron sequences facilitates 59 splice site recognition by U1 snRNP on some pre-mRNAs (Del Gatto-Konczak et al+, 2000;Forch et al+, 2000;Le Guiner et al+, 2001)+ In the case of the adenovirus L1 splicing unit, the binding of ASF/SF2 immediately upstream of the branch site flanking the IIIa exon sterically prevents U2 snRNP binding and hence represses splicing (Kanopka et al+, 1996)+ Likewise, hnRNP I/PTB has been found to antagonize the binding of U2AF to some 39 splice sites (Valcárcel & Gebauer, 1997)+ In other situations, exon enhancer elements bound by SR proteins can promote inclusion of an exon by stimulating the interaction of U2AF and/or U2 snRNP with the 39 splice site region (reviewed in Tacke & Manley, 1999;Graveley, 2000)+ Although some control elements do not affect the initial recognition of splicing signals (Gontarek et al+, 1993;Chou et al+, 2000), the exact mechanism by which many elements and regulatory factors affect splice site selection is currently unknown+…”