THE ROLES OF THE BACTERIOPHAGE-T4 R-GENES IN LYSIS INHIBITION AND FINE-STRUCTURE GENETICS - A NEW PERSPECTIVE

Seldom has the study of a set of genes contributed more to our underst anding of molecular genetics than has the characterization of the rapi d-lysis genes of bacteriophage T4. For example, T4 rII mutants were us ed to define gene structure and mutagen effects at the molecular level and to help unravel the genetic code. The large-plaque morphology of these mutants reflects a block in expressing lysis inhibition (LIN), t he ability to delay lysis for several hours in response to sensing ext ernal related phages attacking the cell, which is a unique and highly adaptive attribute of the T-l family of phages. However, surprisingly little is known about the mechanism of LIN, or how the various r genes affect its expression. Here, we review the extensive old literature a bout the r genes and the lysis process and try to sort out the major p layers affecting lysis inhibition. We confirm that superinfection can induce lysis inhibition even while infected cells are lysing, suggesti ng that the signal response is virtually instantaneous and thus probab ly the result of post-translational regulation. We identify the rI gen e as ORF tk.-2, based on sequence analysis of canonical rI mutants. Th e rI gene encodes a peptide of 97 amino acids (M-r = 11.1 KD; pI = 4.8 ) that probably is secreted into the periplasmic space. This gene is w idely conserved among T-even phage. We then present a model for LIN, p ostulating that rI is largely responsible for regulating the gpt holin protein in response to superinfection. The evidence suggests that the rIIA and B genes are not directly involved in lysis inhibition; rathe r, when they are absent, an alternate pathway for lysis develops which depends on the presence of genes from any of several possible prophag es and is not sensitive to lysis inhibition.