A comparitive analysis of RNA coliphages: structural and regulatory features

Describes a comparative analysis of RNA coliphages with special emphasis on regulatory and structural features. Phylogenetic phage sequence comparison reveals kinship between different phages and facilitates deduction of their secondary structure. Complete sequences from phage fr and partial sequences from group I phages M12, R17 and f2 were determined. The nucleotide sequence from a serological intermediate JP34 was partially elucidated, Only the fr sequence proved suitable for comparison with MS2 (similarity 77 per cent). A "core" structure (3' terminal region) of phage RNA proposed a certain structural resemblance with tRNA. Comparison of the MS2 and fr nucleotide sequences revealed absence of an AUG initiator codon for the fr lysis (L) gene. However, 4 codons further downstream there is a UUG codon which proved to be the start codon for the fr lysis gene. This UUG start codon proved crucial for L-gene regulation. It is suggested that terminated but not released ribosomes mediate the L-gene activation. A general eubacterial scanning model is proposed. It seems that ribosomes can scan the mRNA in both directions and reinitiate at the first encountered restart site. This eubacterial scanning model parallels the eukaryotic translation initiation mechanism

The ecophysiology of bacteriophage infecting halophilic archaebacteria

An ecophysiological study of halophages, isolated from the Yallahs Salt Ponds, Jamaica, has been performed to determine (i) what effect, if any, the single most important environmental parameter, salinity, has on phage-bacterium interactions, and (ii) which phage functions and phage-bacterium interactions are most likely to be of long term significance to the co-existence of halophage and halobacteria in nature. Results indicate that the NaCl concentration governs the interactions between halophages and the extremely halophilic strains of halobacterium. Phage growth is invariably attentuated at high salinity. A more detailed study on a single phage isolate, S5100, shows that at high salinities the maturation of phage is repressed, and lytic phage infections give way to persistent infections. In most instances, the frequency of productive infections initiated by each phage on each sensitive host strain is a consistent function of the host rather than the phage. Closer inspection revealed that the intracellular stages of the phage infection process have a higher degree of host specificity than the cellular receptor sites. It has been demonstrated that mutations to higher virulence and/or extended host range occur in the morphological group A1 phages. Phage absorption is implicated as the stage of the phage infection process that is affected by these mutations. The group B1 halophage, S45, is restricted and modified in vivo by strains of Halobacteriums. Three strain-specific activities have been observed. Two of these occur in the same bacterial strain and appear to be due to different kinds of enzymatic activities. One of the restriction specificities is shown to be associated with a strain-specific endonuclease active on unmodified halobacterial DNA. These phenomena that have been observed are discussed with respect to possible implications for phage ecology and evolution (AU)