The morphogenesis of bacteriophage lambda: IV. Identification of gene products and control of the expression of the morphogenetic information

Abstract

The synthesis of λ-coded proteins has been examined in infected cells in which host protein synthesis was depressed by previous irradiation with uv light. Labeled proteins were analyzed by electrophoresis in polyacrylamide gels containing sodium dodecylsulfate, and the pattern of radioactive bands was visualized by autoradiography of dried longitudinal gel slices. More than 30 viral proteins were identified; 15 of these were assigned to cistrons in the morphogenetic region, three to cistrons in the b region (or silent region) and three were under control of the early genetic region between the att site and cistron N. Among the 15 late proteins assigned to cistrons, nine were structural components of the phage particle. A kinetic analysis of the amounts of gene products, as measured by microdensitometry, indicated that the synthesis of individual late proteins in phage λ seems to be initiated in an orderly fashion, related to the distance of the genes from the late main promoter between genes Q and S. Absence of gene Q product resulted in a sevenfold depression in the synthesis of late proteins, including the late proteins of the b region. Only three polar effects were demonstrated in the left arm. These included the group of cistrons EF, VGTH and LK. The number of copies of gene products synthesized by the different genes in the morphogenetic region was not related in a simple way to the distance of the genes from the main late promoter and may vary by up to a factor of 870. This indicates the presence of a remarkable control mechanism for gene expression of the left arm. Evidence has also been obtained for the conversion of one late protein during λ development, probably by proteolytic cleavage. Measurement of the molecular weights of the assigned late proteins has allowed the construction of a composite genetic, physical and molecular map of the left arm of phage λ. On this basis it is predicted that the gene products of the genes for which no corresponding electrophoretic band has yet been found will be of small molecular weight.