The resistance (R)-factor R538–1drd of three F-like R-factors tested can cause the transfer of the non-transmissible ColV determinant from E. coli V. The col factor, once transferred to E. coli K-12 strains, was shown to be related to the fertility factor, F, on the basis of entry exclusion and plasmid incompatibility. The col factor was found to recombine with R538–1drd, yielding a transmissible plasmid comprised of the col determinant and the sex factor of the R-factor, but not the resistance genes. The recombinant plasmid was found to be incompatible with both R538–1drd and F, and excluded the entry of R538–1drd but not F.

Strains of Escherichia coli which contain the UV sensitivity gene exrA, repress UV induction of λ prophage in a novel manner. While exrA+ strains can be induced by UV irradiation and express this induction in a 2 h period, exrA mutants delay the expression of induction for almost 4 h, and the induction maximum is approximately 10% of the wild-type value. The kinetics of the delayed induction and superinfection experiments indicate that the lifting of immunity and induction of λ prophage occur simultaneously.

Hairs from two stocks of homozygous waved-2 mice have been examined. The observations do not agree with a previous report, that the waving was due to a decrease in the proportion of guard hairs and an increase in the number of constrictions per hair, but are consistent with the view that it arises from a defect of keratinization.

Derepressed mutants of F-like transfer factors, isolated by mutagenesis, were characterized as repressor-minus (i−) or operator-constitutive (oc). Mutants of the i− class are derepressed in K12 but repressed in Salmonella typhimurium. They are derepressed in S. typhimurium by a kanamycin resistance determinant carrying a locus der, described previously. Most oc mutants of F-like factors are derepressed in both K 12 and S. typhimurium. However, one mutant of F-lac was oc in K12 but was repressed in S. typhimurium. It was derepressed by der. Repression by S. typhimurium is different from that by fi+ factors, since der reverses the former but does not affect the latter. Possible interpretations of these findings are discussed.

A technique using microserological equipment is described whereby up to 144 quantitative interrupted bacterial matings may be performed concurrently. The technique is easy to use, accurate and reproducible, and eliminates the need for agar plates. However, it is only suitable for 40–42 °C matings and mating efficiency is approximately threefold lower than in test tubes.

A spontaneous mutant of Phytophthora drechsleri, resistant to p-fluorophenyl-alanine and two induced mutants resistant to chloramphenicol have been selected and analysed. The pattern of inheritance of the mutant phenotypes was identical and conformed to that expected in a diploid organism.

R factors present in Pseudomonas aeruginosa strains of clinical origin can be transferred to other strains of P. aeruginosa and may act to promote host chromosome transfer. In general, their properties are similar to those R factors in Enterobacteria. The different R factors studied vary with respect to transferability, transfer of specific resistance properties, repressibility, and ability to promote chromosome transfer.

The fi+ (fertility inhibition+) property was originally described in R factors related to F (F-like factors). The original fi− factors, in contrast, were related to the transfer factor of a colicin I factor (I-like factors). We describe here a group of R factors which are fi+ but I-like. It is suggested that all the terms fi+, fi−, F-like and I-like be used in the description of transferable plasmids.

Mutants of Aspergillus nidulans unable to use either the choline moiety or the sulphate moiety of exogenous choline-0-sulphate have been selected. Choline-0-sulphate non-utilizing (csu) mutations have no other apparent pleiotropic effects, but it has not yet been established whether they lead to loss of choline sulphatase (and thus of the ability to utilize endogenously produced choline-0-sulphate) or to loss of a specific transport system for choline-0-sulphate or to loss of both.

The problem of replica plating filamentous fungi such as Coprinus lagopus is overcome by inducing micro-colonies with sodium deoxycholate and using ‘Velcro’, a hooked material, to replace velveteen in the standard replica plating technique. ‘Velcro’ is advantageous in that it has a regular pattern of closely spaced hooks which transfer small inocula from the colonies on the master plate.