Genetic mapping of the G101 bacteriophage (Pseudomonas aeuruginosa by temperature-sensitive mutations

Temperature-sensitive (ts) mutations of the G101 phage were isolated after mutagenesis with hydroxylamine. A complementation analysis of 61ts mutants showed that these mutants may be divided into at least 12 complementation groups. Twots mutants probably originated in genes which control lytic functions of the G101 phage. It was shown by three factor crosses that all of the 12ts mutations tested are localized on that side of the “c” region where the probablecI repressor gene is positioned. Sevents mutations is closely linked to thecI ₂₆ clear marker, three exhibit a closer linkage and two do not exhibit any linkage withcI. All mutations isolated until now can be arrange linearly. According to the present knowledge the preliminary genetic map of the G101 phage is linear.     

Thermal melting and circular dichroism of DNA complexes with (Lys-Ala-Ala)10 and (Lys-Ala-Ala)n: effect of polypeptide chain length

DNA complexes with polypeptides (Lys-Ala-Ala)₁)] and (Lys-Ala-Ala)₃₄ have been studied using the methods of thermal melting and circular dichroism. Derivative melting curves of (Lys-Ala-Ala)₁₀ DNA differed substantially from those of (Lys-Ala-Ala)₃₄ prepared either by salt gradient dialysis or by direct mixing. Melting curves of the former complex were unimodal or bimodal with T_m increasing continuously withn input lysin-to-DNA phosphate ratio (r); those of the latter complex consisted of three separate transitions with T_m values almost independent of r. Complete reversibility of binding in the (Lys-Ala-Ala)₁₀-DNA system but a slow redistribution of (Lys-Ala-Ala)₃₄ on DNA at low temperature were found in the redistribution experiments Much faster redistribution from denatured to native DNA occurs at the temperature of melting, contributing to the unusual trimodal melting pattern. Circular dichroism curves are very similar for both complexes and indicate little change of DNA conformation upon polypeptide binding.     

Oogenesis in the Apogamous Fern Pteris cretica

The events that characterize egg formation and maturation inPteris cretica were investigated using transmission electronmicroscopy and electron microscope microprobe analysis. Theydid not differ significantly from those described for sexuallyreproducing ferns. The significance of these findings is discussedin relation to current theories concerning phase change in ferns. Pteris cretica, fern, apogamy, agamospory, transmission electron microscopy, oogenesis     

The dsRNA ofTrichomonas vaginalis is associated with virus-like particles and does not correlate with metornidazole resistance

Twelve metronidazole-resistant and twelve metronidazole-susceptible strains ofTrichomonas vaginalis were tested for the presence of dsRNA. Three resistant and five susceptible strains were found to contain dsRNA which indicated that metronidazole resistance does not correlate with the absence of dsRNA. Electron microscopy showed the homogenates of all dsRNA -positive strains to contain virus-like particles 32 –38 nm in diameter, while no such particles were found in the dsRNA-negative strains. A mutual relationship between the dsRNA and virus-like particles seems to exist. After this paper had been accepted for publication the occurrence of virus-like particles in dsRNA-positive trichomonads was reported by others (Wang A.L., Wang C.C.: The double stranded RNA inTrichomonas vaginalis may originate from virus-like particles.Proc. Nat. Acad. Sci. USA 83, 7956–7961, 1986).