Arrest of Host Cell Development,Replication,Transcription,Translation,Gene Expression,Replicative Cell Synthesis

Arrest of Host Cell Development

	Arrest of Host Cell Development - The T-even phages bring about complete arrest of host cell nucleic acid synthesis and protein synthesis, i. e. there is arrest of replication, transcription and translation. It was earlier thought that cessation of host gene expression was the result of breakdown of its DNA. However, it was shown that 5 minutes after T4 infection the bacterial chromosome has undergone only partial breakdown, and that the fragments are still larger than the T4 chromosome. Protein synthesis, however, stops three minutes after infection.
Host DNA synthesis continues at a substantial level up to at a least 10 minutes after infection at 37°C (Scofield, et. al, 1974). This synthesis is primarily, nonconservative (repair) synthesis. It is an attempt by the bacterial cell to repair the damage caused by phage-coded nucleases. Replicative host cell synthesis occurs only 10 the early stages of infection. Host DNA arrest is caused primarily by DNA fragmentation. Several causes have been suggested for arrest of bacterial cell gene expression. ltered strains or change in fermentation conditions have been partially successful.
(i) Degradation of host DNA by phage coded nucleases (DNA fragmentation) appears to be the primary cause of host DNA arrest. (ii) Ghost infection. The phages remain bound to the cell surface but do not inject anything. Cell substances leak out through the punched holes, thus impairing replication. (iii) The RNA polymerase is modified, so that it initiates transcription preferentially in the phage rather than the, host.
(iv) There are changes in the translation apparatus. The ribosomes are altered because of the association of several new proteins with them.

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Arrest of Host Cell Development