The expression of two classes of late genes of bacteriophage T4

Activation of herpes simplex virus 1 gamma 2 genes by viral DNA replication

The expression of gamma 2 or true gamma genes resident in the herpes simplex virus 1 genome requires functional products of genes expressed earlier in infection and viral DNA synthesis. To determine whether the requirement for viral DNA synthesis for the expression of gamma 2 genes reflects a trans-acting function of a product of one or a few genes made or activated during viral DNA synthesis or whether it reflects a cis effect of DNA synthesis at specific sites, 143 thymidine kinase (TK) minus cells were sequentially infected with a virus carrying a 700-bp deletion of the TK gene and 6 hr later with wild-type or recombinant viruses carrying an alpha-TK or a gamma 2-TK gene in either the presence or absence of viral DNA synthesis. These experiments indicated that the gamma 2-TK gene contained in an unreplicated viral genome was not expressed by trans-acting factors specified before and during DNA synthesis by the first infecting virus, and, therefore, the induction of gamma 2 genes appears to be mediated by a cis-acting function associated with viral DNA synthesis.

Activation of the adenovirus 2 protein IX promoter by DNA replication in a transient expression assay

We have studied the effect of template replication on transcriptional activation of the promoters for the adenoviral protein IX and E1a genes using a short-term transient expression assay. DNA replication mediated modulation of the transcriptional activity of these promoters was monitored using plasmids with limited replication capability conferred by the SV40 minimal origin of DNA replication in the monkey kidney cell line, COS M6. Our results indicate a substantial increase in protein IX promoter directed transcription in a dosage-independent manner as a consequence of the DNA replication process. In contrast, the transcriptional activity of the adenovirus 2 E1a promoter was not significantly altered. In addition to this DNA replication-mediated effect, transcription from the protein IX promoter was positively regulated by the adenovirus E1a 13S and E4 gene products but was repressed by the E1a 12S gene product to a limited extent. The evidence suggests that the effect of template replication on the transcriptional activity of plasmid-borne protein IX and E1a gene promoters in this transient expression system closely mimics the situation on the viral chromosome.

DNA replication and the early to late transition in adenovirus infection

Expression of the late genes of adenovirus is only detectable after virus DNA synthesis has occurred. Using a superinfection protocol, we show that replication of the template per se is required for expression of late regions L2--L5 (mapping to the right of position 39) and that the accumulation of early gene products does not suffice. This regulation is probably exerted at the level of transcription rather than by control of processing or selective stabilization of late mRNA or its precursors. The promoter-proximal late gene block L1, however, appears to be subject to processing control. At early times a single member of this gene family (tripartite leader plus coordinates 29--39, encoding the 52,55K polypeptide pair) is expressed, whereas at late times an additional, differently spliced mRNA species is generated from this region (tripartite leader plus coordinates 34--39, encoding polypeptide IIIa).

Bacteriophages of Bacillus subtilis

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Regulation of expression of late genes of bacteriophage T5

Amber mutants of bacteriophage T5 defective in gene C2 have been characterized. The product of this gene is required for the normal turn-on of synthesis of late RNA's and proteins, and, apparently, for the normal continued synthesis of early RNA's and proteins during late stages of infection. The inability of nonpermissive cells to synthesize any proteins, either late or early, during the late period after infection with a C2-mutant is not due to premature lysis of the infected cells, to a depletion of the cellular energy supply, or to degradation of phage DNA at late times. A possible role for the product of gene C2 in early and late transcription of the viral genome is suggested.

Requirement of a phage-induced 5'-exonuclease for the expression of late genes of bacteriophage T5

Amber mutants of bacteriophage T5 defective in gene D15, which codes for a 5'-exonuclease, do not express late genes. Electrophoretic separation in sodium dodecyl sulfate-polyacrylamide gels of the proteins induced by this mutant in nonpermissive Escherichia coli show a virtual absence of late proteins. Synthesis of lysozyme and serum-blocking power is very low whereas the extent of synthesis of an early enzyme, deoxyribonucleoside monophosphokinase, is similar to that in wild-type infections. It is proposed that one requirement for the expression of late T5 genes is the introduction of gaps or nicks in the T5 DNA so that late transcription can occur.

Transforming ability of a T4 RNA-DNA copolymer

A coliphage T4-specific RNA-DNA copolymer is genetically competent to transform a marker in gene 43, the DNA polymerase.

Nucleic acid synthesis in bacteriophage SPO2c 1 -infected Bacillus subtilis

The synthesis of host macromolecules was shut off very slowly and incompletely by bacteriophage SPO2c(1). No change in the rate of incorporation of radioactive precursors into protein and ribonucleic acid (RNA) could be detected after infection, and the rate of incorporation of thymidine was increased only slightly. The relative proportions of phage and host species of nucleic acids at various intervals in the latent period were determined by means of nucleic acid hybridization. Phage-specific RNA populations synthesized early were different from those synthesized late in the latent period. Host deoxyribonucleic acid (DNA) replication continued until 8 to 10 min after SPO2c(1) infection and then decreased markedly as phage-specific DNA synthesis was initiated. Host DNA was not degraded to trichloroacetic acid-soluble fragments, and its nucleotides were not found in either newly synthesized intracellular phage DNA or in progeny phage particles. The average burst size of SPO2c(1) was approximately 200 plaque-forming units per cell.

Synthesis of virus-specific ribonucleic acid in KB cells infected with type 2 adenovirus

By using the technique of deoxyribonucleic acid (DNA)-ribonucleic acid (RNA) hybridization, virus-specific RNA (cRNA) was detected 6 hr after infection in preparations of total RNA from cells infected with type 2 adenovirus in the presence of 2 mum 5-fluorodeoxyuridine. In the absence of 5-fluorodeoxyuridine, there was a continuous increase in the incorporation of (3)H-uridine into viral cRNA until 20 hr after infection, at which time approximately 40% of the (3)H-uridine entering RNA was found in virus-specific RNA. When RNA was prepared from polyribosome fractions obtained from cytoplasmic extracts of infected cells, virus-directed transcription was detected at 3 hr after infection (i.e., 3 to 4 hr before the initiation of viral DNA synthesis). Viral cRNA species synthesized at different times after infection were compared by the technique of DNA-RNA hybridization-inhibition ("presaturation" hybridization-competition). Three hybridization-inhibition techniques were compared. The techniques differed in the manner in which the DNA-RNA complex was isolated after the first hybridization reaction. Depending on the procedure employed, various degrees of inhibition were measured. The variation could be essentially eliminated if prior to hybridization the inhibitory RNA species were alkali-degraded to a uniform size of about 4S. Undegraded RNA could be used if the DNA-RNA complex was isolated by using a procedure involving rigorous washing (preferably including ribonuclease treatment) before the second hybridization with labeled RNA. When a rigorous hybridization-inhibition procedure was used, three classes of virus-specific RNA species could be distinguished: (i) early RNA class I whose synthesis began prior to viral DNA replication and stopped at some time after the initiation of viral DNA replication-it comprised about 70% of the early RNA species and was apparently degraded by 18 hr after infection; (ii) early RNA class II whose synthesis began prior to viral DNA replication and apparently continued at an enhanced rate late in infection; and (iii) late RNA whose synthesis began after the initiation of viral DNA synthesis.