Insertion elements and transitions in cloned mouse mammary tumour virus DNA: further delineation of the poison sequences

Abstract

The provirus of mouse mammary tumour virus (MMTV) is reputed to contain sequences within the viral gag gene that prevent or inhibit its propagation as a recombinant DNA clone in Escherichia coli. Here we report the successful isolation of several lambda and plasmid clones comprising the 5' virus-host DNA junction fragments from integrated MMTV proviruses in BR6 mice. Although the lambda clones appeared intact, almost all of the plasmids were found to contain the bacterial insertion sequences IS1 or IS2 within a small region of the gag gene. One nondisrupted clone was recovered which had undergone multiple G to A transitions, some of which created stop codons in gag. These results have provided more precise information as to the location of the poison sequences and are discussed in relation to possible explanations for the phenomenon.

C3H strain of mouse mammary tumour virus, like GR strain, infects human mammary epithelial cells, albeit less efficiently than murine mammary epithelial cells

“…We designated these viruses MMTV(C3H)hp1 and MMTV(GR)hp1. Comparison of 10 complete MMTV(C3H)hp1 and MMTV(GR)hp1 proviral sequences (minus the gag gene, which contains a poison sequence; Brookes et al, 1986) with MMTV(C3H) and MMTV(GR) sequences identified in virus preparations from murine mammary carcinoma cells, respectively, revealed that MMTV(C3H)hp1 and MMTV(GR)hp1 did not contain sequences from other viruses, the mouse genome [including endogenous mouse mammary tumour proviruses (Mtvs)] or the human genome ( Fig. S2 and data not shown).…”

Cloning and characterization of the white gene from Anopheles gambiae

“…Comparison of the 5'-end of the cDNA with genomic sequences revealed three occurrences of the pentamer (G/C)CAGT in the 52 bp of genomic sequence immediately flanking the first nt of the cDNA. The eukaryotic capsite consensus sequence TCAGT occurs in 25% of arthropod polymerase Il-transcribed promoters within 10 bp of the transcription start site (Cherbas & Cherbas, 1993). It has been suggested that this capsite consensus sequence and, less frequently, its variants (A,G,C)CAGT may be initiators (Cherbas & Cherbas, 1993).…”

“…The eukaryotic capsite consensus sequence TCAGT occurs in 25% of arthropod polymerase Il-transcribed promoters within 10 bp of the transcription start site (Cherbas & Cherbas, 1993). It has been suggested that this capsite consensus sequence and, less frequently, its variants (A,G,C)CAGT may be initiators (Cherbas & Cherbas, 1993). However, the assignment of the transcription start site awaits further experiments.…”

Reverse transcriptase of mouse mammary tumour virus: expression in bacteria, purification and biochemical characterization

“…MMTV was the first mammalian retrovirus to be isolated. Among the retroviruses, MMTV is highly refractory to molecular studies owing to technical obstacles, which stem from two main reasons : a strong tropism to mammary alveoli cells (which are difficult to grow in cell cultures) and resistance to molecular cloning of the full-length proviral DNA [9][10][11]. This might explain why MMTV RT has not so far been expressed as a recombinant protein and why the only reports on the catalytic properties of the partly purified virus-derived RT preparations were published more than 20 years ago [12,13].…”