A Novel DNA Polymerase Activity Found in Association with Intracisternal A-Type Particles

Wilson, Samuel H.; Kuff, Edward L.

doi:10.1073/pnas.69.6.1531

Cited by 71 publications

(47 citation statements)

References 20 publications

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“…IAPs have reverse transcriptase activity (13) and contain polyadenylylated RNA of 3.5 to 7 kilobases (kb) (14,15), which codes for the major particle protein p73 (14). There are 1,000 TAP genes (provirus-like genetic elements) per haploid mouse genome (15)(16)(17), and genomic clones of several of these have been isolated and analyzed (15,18,19).…”

Section: Iap(s)] Using Cloned Fragments Of Iap Genes As Labeledmentioning

confidence: 99%

Amounts, synthesis, and some properties of intracisternal A particle-related RNA in early mouse embryos.

Pikó¹,

Hammons²,

Taylor³

1984

Proc. Natl. Acad. Sci. U.S.A.

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Early mouse embryos express two morphological subtypes of intracisternal A-type particles, one resembling those occurring in mouse tumors (referred to as IAP) and the other apparently specific for early embryos [referred to as IAP(s)]. Using cloned fragments of IAP genes as labeled probes in dot-hybridization experiments, we detected IAP-related RNA sequences in mouse oocytes and preimplantation embryos. IAP RNA is relatively abundant in ovarian oocytes, is reduced in amount to l1/10th in the ovulated erg, and increases f100 times (from -1.3 x 103 to -1.5 x 10 molecules per embryo) between the one-cell stage and late blastocyst stage. Most of the IAP RNA consists of a single size class of about 5.4 kilobases, and a major fraction of this RNA is polyadenylylated. Quantitative considerations suggest that only a few percent of the IAP RNA in embryos are associated with particles. In two-cell embryos, the number of IAP RNA molecules is <1/10th the number of IAP(E) particles, suggesting that IAP(E) is genetically distinct from IAP and presumably represents a family of as yet unidentified retrovirus-like elements.Early mouse embryos regularly express several types of virus-like structures whose appearance is correlated with specific stages of development (for review, see refs. 1 and 2). Intracisternal A-type particles (IAPs), of which two morphological subtypes have been distinguished (3,4), are the most prominent. Particles of one subtype, termed "small A particles" (3) or, more recently, "s-particles" to emphasize their distinctness (4), seem to be specific for early embryonic cells and form in large clusters in two-to eight-cell embryos but are absent or sparse at other stages (3-7). We will refer to these particles as IAP(E)s. The other subtype, designated "large A particles" by Chase and Pik6 (3) (3,4). In this report, we will restrict the term UAP to this second type of A particle. The role of either subtype of A particle in embryo development is unclear at present, but there is evidence for the cell-surface expression of IAPrelated antigens in early embryonic cells (9, 10).The IAPs found in tumor cells have many properties resembling those of infectious retroviruses, but IAPs are genetically distinct from the mouse type B and type C viruses (11,12). IAPs have reverse transcriptase activity (13) and contain polyadenylylated RNA of 3.5 to 7 kilobases (kb) (14, 15), which codes for the major particle protein p73 (14). There are 1,000 TAP genes (provirus-like genetic elements) per haploid mouse genome (15)(16)(17), and genomic clones of several of these have been isolated and analyzed (15,18,19). The predominant gene form is 7 kb in length (18, 19), but shorter units with major deletions and substitutions also have been found (15,17). IAP genes are bordered by direct long terminal repeats (LTRs) of about 0.35 kb, which are similar in structure to the proviral LTRs of infectious retroviruses (20, 21). IAP gene insertions were found in two mutant mouse K light-chain genes (21) and in a cellular oncogene (22),...

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Section: Iap(s)] Using Cloned Fragments Of Iap Genes As Labeledmentioning

confidence: 99%

Amounts, synthesis, and some properties of intracisternal A particle-related RNA in early mouse embryos.

Pikó¹,

Hammons²,

Taylor³

1984

Proc. Natl. Acad. Sci. U.S.A.

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“…They contain a group-specific internal structural protein, p73 (20,32), and a DNA polymerase activity with properties of reverse transcriptase (42,43). The isolated particles also contain specific polyadenylated [poly(A)] RNAs (30) ranging in size from 7.2 to about 3.5 kilobases (kb) (34,36,41).…”

mentioning

confidence: 99%

Intracisternal A-particle gene expression in normal mouse thymus tissue: gene products and strain-related variability.

Kuff¹,

Fewell²

1985

Mol. Cell. Biol.

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Intracisternal A-particle (IAP)-specific sequences were 5-to 10-fold enriched in polyadenylated RNA from BALB/cJ thymus as compared with RNAs from liver, spleen, and kidney. The major transcripts of 7.2 and 5.4 kilobases were the same size as those found in an TAP-rich neuroblastoma cell line. The absolute levels and proportions of these transcripts varied in thymuses from mice of different inbred strains. With antiserum prepared against p73, the main IAP structural protein, several size classes of IAP-related proteins were immunoprecipitated from extracts of thymus cells incubated with [35S]methionine; these included p73 itself and a group of polypeptides in the size range of 114 to 120 kilodaltons (pll4-pl20). The inbred strains showed marked characteristic differences in the electrophoretic patterns of their IAP-related proteins. Earlier studies showed that the 7.2-kilobase RNA from neuroblastoma IAPs coded for p73 in a cell-free translation system. Correlations between the RNA and protein patterns in thymuses of the different inbred strains indicated that 5.4-kilobase RNA gives rise to the pll4-pl20 polypeptides. Metabolically labeled p120 was found to include methionine-containing tryptic peptides of p73 plus additional peptides consistent with its larger size. In vivo labeling kinetics showed that the pll4-pl20 polypeptides were not major precursors of p73 in intact neuroblastoma cells. This study shows that IAP gene expression in mouse thymus is genetically determined and that a novel class of IAP-related polypeptides can be expressed independently of the major particle structural protein.Intracisternal A-particles (IAPs) are retrovirus-like entities found in many types of mouse tumor cells (20,45). They contain a group-specific internal structural protein, p73 (20,32), and a DNA polymerase activity with properties of reverse transcriptase (42, 43). The isolated particles also contain specific polyadenylated [poly(A)] RNAs (30) ranging in size from 7.2 to about 3.5 kilobases (kb) (34,36,41). These RNA species, which are related to one another in sequence, vary in relative proportion in particles isolated from different tumor sources. Endogenous provirus-like elements homologous to the IAP-associated RNAs ("IAP genes") are reiterated 1,000-fold per haploid genome in Mus musculus (28). The full-size genetic unit is 7.3 kb in length and is colinear with the 7.2-kb transcript (21). Shorter elements with internal deletions are also found (21, 34), and one group of these, the so-called type IT elements (40), are known to give rise to some of the shorter IAP-specific RNAs (34, 41). The IAP genetic elements share many structural properties with integrated retroviral proviruses and certain transposable elements in Drosophila spp. and yeasts (8a). Recently, IAP genes have been found to appear in novel locations in the genome of certain IAP-rich BALB/c mouse myeloma and hybridoma cell lines and to affect the function of genes at the various target sites (5,7,9,10,18,19,41). Thus, on occasion they can act as mobile e...

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“…They are characterized by long terminal direct repeats whose structure is intimately involved in the transposition process. They also encode reverse transcriptases which may be involved in their transposition (29,45,58).…”

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confidence: 99%

Ingi, a 5.2-kb dispersed sequence element from Trypanosoma brucei that carries half of a smaller mobile element at either end and has homology with mammalian LINEs.

Kimmel¹,

ole-MoiYoi²,

Young³

1987

Mol. Cell. Biol.

172

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A dispersed repetitive element named ingi, which is present in the genome of the protozoan parasite Trypanosoma brucei, is described. One complete 5.2-kilobase element and the ends of two others were sequenced. There were no direct or inverted terminal repeats. Rather, the ends consisted of two halves of a previously described 512-base-pair transposable element (G. Hasan, M. J. Turner, and J. S. Cordingley, Cell 37:333-341, 1984). Oligo(dA) tails and possible insertion site duplications suggested that ingi is a retroposon.The sequenced element appears to be a pseudogene copy of an original retroposon with one or more open reading frames occupying most of its length. Significant homologies of the encoded amino acid sequences with reverse transcriptases and mammalian long interpersed nuclear element sequences suggest a remote evolutionary origin for this kind of retroposon.

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A Novel DNA Polymerase Activity Found in Association with Intracisternal A-Type Particles

Cited by 71 publications

References 20 publications

Amounts, synthesis, and some properties of intracisternal A particle-related RNA in early mouse embryos.

Amounts, synthesis, and some properties of intracisternal A particle-related RNA in early mouse embryos.

Intracisternal A-particle gene expression in normal mouse thymus tissue: gene products and strain-related variability.

Ingi, a 5.2-kb dispersed sequence element from Trypanosoma brucei that carries half of a smaller mobile element at either end and has homology with mammalian LINEs.

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