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Based on our work in the past 10 years, we have concluded that mouse embryonic stem cells are "quasi-totipotent" in vitro; that is, they resemble and may even possess the full totipotency of germ c...

The B. subtilis bacteriophage SPP1 terminase, encoded by genes 1 and 2, is required for the initiation of headful packaging. The DNA segment to which gene 1 product (G1P) binds includes the pacL and pacR sites and the late PL1 and PL2 promoters from which genes 1 to 7 are transcribed. When SPP1wt or SPP1sus115 (gene 6−) phages were used to infect a B. subtilis sup0 strain, the gene 1 to 7 mRNA synthesis was reduced at late times of infection. This was not observed, however, when either chloramphenicol was added 7 min after infection with SPP1wt or when SPP1sus114 (gene 1−) or SPP1sus19 (gene 2−) were used to infect B. subtilis sup0 cells. These results suggest that the terminase enzyme functions as a repressor of its own transcription. G1P and B. subtilis RNA polymerase (RP) bind to the pacL segment, which contains the PL1 and PL2 promoter region. The binding of G1P to the pacL site does not seem to exclude RP from the promoters, despite of the overlapping of their binding sites. It is likely that the terminase protein does not repress transcription by a mere steric hindrance of RP binding.

The left end of the genome of Bacillus subtilis bacteriophage SPP1 is represented by EcoRI DNA fragments 12 and 1 (EcoRI-12 and EcoRI-1). A number of different deletions were identified in EcoRI-1. A detailed physical and genetic map of EcoRI-1 from wild-type (wt) phage and SPP1 deletion mutants was constructed. Genes encoding essential products involved in late and early stages of phage DNA metabolism were mapped at the left and right ends of the 8.5-kb EcoRI-1, respectively. Deletions fell within the internal 5157-bp DNA segment of EcoRI-1. The nucleotide (nt) sequence of this region and of the endpoints of two deletions, delta X and delta L, were determined. The nt sequence of the junctions in SPP1 delta X and SPP1 delta L showed that, in these deletions, a segment of DNA between short directly repeated sequences of 10 and 13 bp, located 3427 and 4562 bp apart in the wt sequence, had been eliminated. In both cases, the copy of the repeated sequence was retained in the deletion mutant, consistent with the hypothesis that the deletions originated by homologous intramolecular recombination. The corresponding region in wt phage had fifteen presumptive open reading frames (orfs) and the previously identified SPP1 early promoters (PE1). The poor growth phenotype associated with the SPP1 deletion mutants was attributed to premature transcriptional read through from promoter(s) of the early region into late operon brought into close vicinity of the late genes due to the deletion event.

The murine cytomegalovirus (MCMV) fcr-1 gene codes for a glycoprotein located at the surface of infected cells which strongly binds the Fc fragment of murine immunoglobulin G. To determine the biological significance of the fcr-1 gene during viral infection, we constructed MCMV fcr-1 deletion mutants and revertants. The fcr-1 gene was disrupted by insertion of the Escherichia coli lacZ gene. In another mutant, the marker gene was also deleted, by recombinase cre . As expected for its hypothetical role in immunoevasion, the infection of mice with fcr-1 deletion mutants resulted in significantly restricted replication in comparison with wild-type MCMV and revertant virus. In mutant mice lacking antibodies, however, the fcr-1 deletion mutants also replicated poorly. This demonstrated that the cell surface-expressed viral glycoprotein with FcR activity strongly modulates the virus-host interaction but that this biological function is not caused by the immunoglobulin binding property.