GENES FOR DNA CYTOSINE METHYLTRANSFERASES AND STRUCTURAL PROTEINS, EXPRESSED DURING LYTIC GROWTH BY THE PHAGE PHI-ETA OF THE ARCHAEBACTERIUM HALOBACTERIUM-SALINARIUM

Lytic genes and transcription from the Halobacterium salinarium phage Phi H were studied. Genes for three structural proteins were located t o the left arm of the linear phage genome. The right arm was shown to encode three DNA cytosine methyltransferases, the first such sequences reported from an archaebacterium. One cytosine methyltransferase is o f the N(4)-methyltransferase type. The other two open reading frames ( ORFs) seem to be parts of the same gene, which has been split by a rec ombination event. This gene product is of the C-5-methyltransferase ty pe. The methyltransferase genes are the first Phi H genes detected sho wing high homology to eubacterial proteins. Five of the six described gene products have a higher proportion acidic over basic amino acid re sidues, a common characteristic of halobacterial proteins. Lytic Phi H transcription was shown to produce three RNA species, two shorter spe cies encoding the methyltransferase genes and one large species transc ribed from both the right and the left phage arm and subsequently bein g processed upstream of the region encoding the structural proteins.