Lys631 residue in the active site of the bacteriophage T7 RNA polymerase. Affinity labeling and site-directed mutagenesis.

A highly selective affinity labeling of T7 RNA polymerase with the o-formylphenyl ester of GMP and [alpha-32P]UTP was carried out. The site of the labeling was located using limited cleavages with hydroxylamine, bromine, N-chlorosuccinimide and cyanogene bromide and was identified as the Lys631 residue. Site-directed mutagenesis using synthetic oligonucleotides was used to substitute Lys631 by a Gly, Leu or Arg residue. Kinetic studies of the purified mutant enzymes showed alterations of their polymerizing activity. For the Lys----Gly mutant enzyme, anomalous template binding was observed.     

The effect of medium acidity on the light-dependent antibacterial activity of fatty acids

The goal of this work was to study how the acidity of a medium influenced the light-dependent antibacterial activity of fatty acids towards Staphylococcus aureus. The antibacterial activity of arachidonic, linolenic, linoleic and oleic acids increased abruptly (by 1-2 orders of magnitude) under the action of visible light, it became more intensive with a rise in the number of double bonds in a fatty acid molecule, and the maximum shifted from the neutral region to an alkaline one as the aeration was intensified. In the case of saturated fatty acids (palmitic and stearic), the antibacterial activity with a maximum in the alkaline region was detected only in the light. The effect exerted by the number of double bonds in a fatty acid molecule and by the acidity of a medium on the mechanisms of fatty acid photooxidation is discussed.     

Effect of cultivation conditions on the activity of the beromycin producerStreptomyces glomeratus 3980 and its spontaneous variants

Optimal conditions for the submerged cultivation ofStreptomyces glomeratus 3980, producer of the anthracycline antibiotics beromycins, and its variants were sought in media with glucose, soybean meal and salts differing in the content of ammonium sulphate. As compared with the original activity of the strain the antibiotic titre of some variants increased about 12 times on increasing the glucose concentration from 3 to 5 %, or on omitting CaCO₃ from the medium (i.e. under conditions leading to an increased production of propionic acid and suppression of production of the melanin-like pigment). In melanin-less variants accumulating propionate even under standard conditions the activity increased about 18–40 times in the medium with 3 % glucose and 0.2 % CaCO₃ under conditions of more intensive aeration (i.e. under conditions when no propionic acid accumulated). Individual strains also differed in the requirement for (NH₄)₂SO₄ in the medium, their response to changes of volume of the vegetative inoculum and sensitivity to MgSO₄.7H₂O. The biosyiithetic activity of all strains was inhibited by the addition of ZnSO₄.7H₂O or CaCl₂ and substitution of glucose with starch, lactose or sucrose.     

Highly selective affinity labeling of DNA-dependent RNA-polymerase II from human placenta

RNA polymerase II from human placenta was affinity labelled in crude preparation using two-step technique, which includes treatment of the enzyme with an aldehyde-containing reactive analogue of ATP, ADP or AMP in the presence of poly[d(A-T)] followed (after borohydride reduction) by the elongation of the attached label with [alpha-32P]UTP. A polypeptide of the molecular mass ca. 140 kDa proved to be the labelling target. No labelling was observed in the absence of poly[d(A-T)] or the reagent or in the presence of alpha-amanitin. All the results suggest the attachment of the affinity reagents to the second-largest subunit of the human RNA polymerase II, which therefore takes part in the initiation substrate's binding.     

Physiological mechanisms of color constancy

Color constancy is the term given to the ability to recognize the color of objects correctly under different conditions of illumination. For this purpose the visual system must determine the character of the illumination, introduce a correction for it into the spectal composition of the light received from the object, and hence recreate the true color of its surface. Behavioral experiments on fish showed that they possess constant color vision of objects. Electrophysiological experiments on ganglion cells of the color type showed that the simplest mechanisms of correction for illumination are found at the retinal level. An investigation of model algorithms providing for color constancy showed thatthe presence of color vision makes it much easier to recognize the three-dimensional form of objects. This fact compels a reexamination of established views regarding the place and role of color vision in functions of the animal visual system as a whole.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 7, No. 1, pp. 21–26, January–February, 1975.     

Biofilm Formation by Monocultures and Mixed Cultures of Alcaligenes faecalis 2 and Rhodococcus ruber gt 1

Microbiology - Biofilm formation by monocultures and mixed cultures of nitrile-hydrolyzing bacteria Alcaligenes faecalis 2 and Rhodococcus ruber gt 1 was studied. Biofilm formation was assessed by...     

Yeast Complexes in Urban Soils of Some Southern Cities of Russia (Krasnodar,Maykop, Simferopol,and Sochi)

Microbiology - Yeast number and species diversity in urban soils characterized by various intensities of anthropogenic impact in the southern cities of Russia (Krasnodar, Maykop, Simferopol, and...