Highly inducible cell lines derived from mice genetically transmitting the Moloney murine leukemia virus genome

Unusual DNA structures associated with germline genetic activity in Caenorhabditis elegans

We describe a surprising long-range periodicity that underlies a substantial fraction of C. elegans genomic sequence. Extended segments (up to several hundred nucleotides) of the C. elegans genome show a strong bias toward occurrence of AA/TT dinucleotides along one face of the helix while little or no such constraint is evident on the opposite helical face. Segments with this characteristic periodicity are highly overrepresented in intron sequences and are associated with a large fraction of genes with known germline expression in C. elegans. In addition to altering the path and flexibility of DNA in vitro, sequences of this character have been shown by others to constrain DNA::nucleosome interactions, potentially producing a structure that could resist the assembly of highly ordered (phased) nucleosome arrays that have been proposed as a precursor to heterochromatin. We propose a number of ways that the periodic occurrence of An/Tn clusters could reflect evolution and function of genes that express in the germ cell lineage of C. elegans.

Differentiation and virus expression in BALB/Mo mice: endogenous Moloney leukemia virus is not activated in hematopoietic cells

The endogenous Moloney leukemia virus (M-MuLV) in the BALB/Mo substrain of mice is activated during the first week after birth. Virus replication occurs in cells of the lymphatic system. Lymphoid cells therefore represent the target cells for virus replication and leukemic transformation. To investigate whether virus activation occurs during lymphoid cell differentiation, hematopoietic stem cells carrying the endogenous Mov-1 genome were transplanted to sublethally irradiated BALB/c mice. Effective colonization of the recipients was demonstrated by Southern DNA hybridization. No activation of the endogenous Mov-1 genome occurred during a 4-month observation period after the transplantation. Thus the first step in development of disease in BALB/Mo mice involves activation of the Mov-1 locus in a nonhematopoietic cell followed by superinfection of lymphatic cells and subsequent virus replication and virus spread.

Integrated Moloney murine leukemia virus DNA studied by using complementary DNA which does not recognize endogenous related sequences

By preannealing a radioactive, representative Moloney murine leukemia virus (M-MuLV) cDNA with large excesses of AKR 70S viral RNA, an M-MuLV-specific cDNA has been prepared. When hybridized to restriction enzyme fragments of M-MuLV-infected mouse cell DNA, the preannealed probe recognizes integrated M-MuLV DNA and does not recognize endogenous related DNA sequences found in uninfected mouse cells. The viral DNA sequences recognized by the preannealed probe are spread throughout the viral genome, although some sequences are recognized less efficiently. By using this preannealed probe, multiple integrations of M-MuLV DNA have been detected in infected fibroblasts and in an M-MuLV-induced tumor. Integrated viral DNA fragments smaller than the complete viral genome have also been detected. By using this preannealed probe to examine a mass-infected culture of mouse fibroblasts, no evidence for a strongly preferred site for M-MuLV integration could be found.

Multiple integration sites for Moloney murine leukemia virus in productively infected mouse fibroblasts

The integration sites for viral DNA in cells infected with Moloney murine leukemia virus (M-MuLV) were studied by restriction endonuclease cleavage of cellular DNA followed by electrophoresis in agarose gels, blot transfer to nitrocellulose, and detection by M-MuLV-related sequences by hybridization with high-specific-activity 32P-labeled M-MuLV complementary DNA. When EcoRI was used to cleave cellular DNA, numerous DNA fragments with sequence homology to M-MuLV were detected in uninfected mouse cell DNA. These endogenous sequences are mouse specific since they are not detectable in rat cell DNA, and are related to the 38S genomic RNA of M-MuLV. Infected cells contain additional M-MuLV-specific DNA fragments which are not detected in uninfected cells. Different patterns of M-MuLV-specific DNA fragments were detected in each cloned infected line examined. These data suggest the existence of multiple sites for integration of M-MuLV DNA in infected mouse fibroblasts. Cleavage of infected cell DNA with BamHI, which cleaves M-MuLV viral DNA at least twice, released the internal BamHI B fragment from each infected line, confirming the presence of integrated M-MuLV DNA sequences in each infected cell line which retain some features of the sequence organization of unintegrated M-MuLV DNA.