Direction of translation in bacteriophage S13

Suppressible (amber-type) mutants in gene IIIa of bacteriophage S13 show polarity in reducing the activity of only the neighboring gene IIIb. The polarity implies that the genome is translated in the direction of IIIa to IIIb. From the known homology of the messenger RNA with the single-stranded DNA, the orientation of the DNA with respect to the genetic map can also be inferred.

Bacteriophage S13: a 7th gene

Genetic complementation tests of ochre-type suppressible mutants of bacteriophage S13 have revealed a seventh gene. A mutation of this gene has no significant effect on synthesis of the phage replicative form DNA, but like five other phage genes it prevents the appearance of single-stranded DNA. With the new gene, it seems likely that approximately 70 to 100 percent of the phage genes are accounted for.

Heat reactivation of the alpha-hemolytic, dermonecrotic, lethal activities of crude and purified staphylococcal alpha-toxin

Manohar, M. (University of Minnesota, St. Paul), S. Kumar, and R. K. Lindorfer. Heat reactivation of the alpha-hemolytic, dermonecrotic, and lethal activities of crude and purified staphylococcal alpha-toxin. J. Bacteriol. 91:1681-1685. 1966.-Crude staphylococcal toxin loses its alpha-hemolytic activity more rapidly at 60 than at 100 C. This paradoxical behavior has been postulated to be due to the presence of a thermolabile inhibitor in crude toxin. This work provides experimental evidence for the presence of a thermolabile "protective inhibitor." This substance(s) protects the alpha-toxin against destruction at 60 C, yet simultaneously inhibits the hemolytic activity of alpha-toxin under the same conditions. Of greater importance, this work also demonstrates that the dermonecrotic and lethal activities of crude toxin are inactivated and reactivated in parallel with the alpha-hemolytic activity. Crude staphylococcal toxin possessing a high alpha-hemolytic titer when heated to 60 C for 30 min lost its alpha-hemolytic, dermonecrotic, and lethal activity. However, when this same toxin was immediately exposed to 100 C, a remarkable simultaneous reactivation of all three of these activities occurred. Contrariwise, electrophoretically purified alpha-hemolysin, which also possessed dermonecrotic and lethal activity, showed no reactivation under these conditions, thus demonstrating that reactivation is due to a substance(s) distinct from the alpha-toxin. The fact that alpha-hemolytic, dermonecrotic, and lethal activities were inactivated at 60 C and simultaneously reactivated at 100 C provides additional proof that these activities are all associated with one toxic component. The probability is remote that three separate entities would exhibit the same rate of inactivation and the same strange reactivation.