Integrated viral sequences

Flanking these structural genes are two direct repeats, the long terminal repeats (LTRs) of about 250 to 1400 base pairs each. Each LTR is flanked in turn by short inverted repeat sequences, 5 to 13 base pairs in length. Integration occurs by a mechanism that duplicates the target site, so that the integrated viral sequence, called a provirus, is flanked by direct repeats of host cell DNA (5 to 13 base pairs each). 

The distribution of integrated viral sequences, transposons and duplicated genes in the mammalian genome... 

The localization of integrated viral sequences in the host genome... 

Another response of most eukaryotic cells to carcinogen-mediated DNA strand breaks is poly(ADP-ribosyl)ation of a variety of nuclear proteins, catalyzed by poly(ADP-ribose) polymerase. We dierefore studied a possible role of poly(ADP-ribose) synthesis in carcinogen-inducible DNA amplification in a SV40 transformed Chinese hamster cell line (CO 60) which shows amplification of integrated viral sequences after carcinogen treatment (5, 7). We found that inhibition of carcinogen-stimulated poly(ADP-ribose) synthesis by 3-aminobenzamide (SAB) is correlated with an enhancement of inducible DNA amplification in CO 60 cells (13). 

Fig. 10. The structure of mouse DNA containing the integrated mouse mammary tumour provirus. The integrated viral DNA can be present in many copies. The provirus contains two long terminal repeat sequences, LTR, only one of which (left) is shown in detail here. Each LTR contains sequences termed U3, R and U5 (for details, see Ref. 67). Interspersed between the LTRs are the genes named gag, pol and env, encoding viral coat proteins, reverse transcriptase and envelope proteins, respectively. The glucocorticoid-binding sequence is represented by the black box, and the transcriptional initiation area is indicated by the hatched box.

To sum up, four retroviruses, three of C-type (BLV, RSV, HTLV-1) and one of D-type (MMTV), were localized in four mammalian species. The data show that integrated retroviral sequences are not spread at random in the host genomes, but are found in some host genome compartments approximately matching the viral sequences in composition. This conclusion is stressed by a presentation of the results in terms of proviral density in host DNA (Fig. 6.5). Expectedly, in none of the cases investigated were the proviral sequences found in satellite or ribosomal DNA. 

The results just presented suggest that (i) integration of pro viral sequences is initially... 

Figure R4(6.4). Distribution of integrated IITLV-I and IIBV viral sequences in the human genotne. The CsCl profile ofhuman liSA is shown. Arrows indicate the GC level of viral sequences, expressed sequences are in red, non-expressed sequences in yellow.

In the central section of the book. Parts 3 and 4 outline the compositional properties of the vertebrate genome, namely the compositional patterns of DNA molecules and of coding sequences, as well as the compositional correlations between coding and non-coding sequences, whereas Parts 5, 6 and 7 discuss the most important properties of the vertebrate genome the distributions of genes, of transposons and of integrated viral... 

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