Sequence variations within protein families are linearly related to structural variations

It is commonly believed that similarities between the sequences of two proteins infer similarities between their structures. Sequence alignments reliably recognize pairs of protein of similar structures provided that the percentage sequence identity between their two sequences is sufficiently high. This distinction, however, is statistically less reliable when the percentage sequence identity is lower than 30% and little is known then about the detailed relationship between the two measures of similarity. Here, we investigate the inverse correlation between structural similarity and sequence similarity on 12 protein structure families. We define the structure similarity between two proteins as the cRMS distance between their structures. The sequence similarity for a pair of proteins is measured as the mean distance between the sequences in the subsets of sequence space compatible with their structures. We obtain an approximation of the sequence space compatible with a protein by designing a collection of protein sequences both stable and specific to the structure of that protein. Using these measures of sequence and structure similarities, we find that structural changes within a protein family are linearly related to changes in sequence similarity.     

Induced variations in microorganisms

Genetic transfer of markers has been found to occur through a sexual cycle between intact cells in a mixed culture of two different genotypes. When rS (radiosensitive and streptomycin resistant) and Rs (radioresistant and streptomycin sensitive) cells ofRhizobium trifolii were brought into varying periods of cellular contact, the cell mixture yielded RS recombinants. The recombination frequency was higher in young mating cultures than in aged ones. Except for the acquisition of the R and S markers, the recombinants did not differ appreciably from the parental strains in other characters.     

Phase variations inBifidobacterium animalis

Strains isolated from rabbit, chicken, and rat feces and from sewage and fermented milk products, all identified asBifidobacterium animalis, were found to show phase variations in colony appearance and in cellular morphology. The rate of transition in a switching system from opaque to transparent colonies and vice versa was determined. Differences in protein components and in penicillin-binding proteins (PBPs) of the cells from different colony types are shown.     

Pachytene variations in Ricinus

The pachytene complement in microsporocytes was compared among ten races of Ricinus communis L., the castor plant (2n=20). Four kinds of pachytene variations were observed: (1) variation in degree of spreading of the chromosomes; (2) variation in degree of attenuation of heterochromatin; (3) variation in morphology, which appeared to be restricted to the two nucleolar organizing bivalents; (4) variation in frequency of association of each of these two bivalents with the nucleolus. It is suggested that variations in the pachytene chromosomes occur ubiquitously in this species.     

Protein variations and primatology

We summarize work based on electrophoretic screening for protein variation within and between primate species. We consider serum proteins—albumins, haptoglobins, transferrins—and red cell proteins—carbonic anhydrases, hemoglobins. Using hemoglobin, cytochrome-c, and fibrinopeptides as examples, we discuss the value of using molecular data, i.e. protein structures, in evolutionary studies and in primatology.     

Induced variations in microorganisms

The mutagenic effect of ultraviolet light on a strain ofRhizobium trifolii T5 was studied. A gradual build-up of radioresistance in the population of the wild cells was observed as a result of cyclic UV irradiation, although there, was no definite indication for a plateau of maximal resistance of the population even after 20 cycles of irradiation. The radio-resistance was built up sooner in a population cycled at a low dose of irradiation (3 sec) than at a high dose (10 sec). The fluctuation test indicated that UV acted as an inducing agent. The frequency of radioresistant cells in a radiation cycled population was about 6.8×10^?6 as against c.4×10^?6 in the nonirradiated population. Five, mutants were examined in detail, in which radioresistance in two was accompanied by resistance to streptomycin also. The mutants did not differ drastically from the wild, strain in their biochemical properties, salt tolerance and clover infectivity. No UV induced auxotrophic mutants were detected.     

Induced variations in microorganisms

Ethyl methanesulfonate was found to be an effective mutagen in inducing auxotrophy inRhizobium trifolii, but ineffective in inducing resistance to streptomycin. The auxotrophic mutants were mostly isolated after the treatment yielding 2–30% survival of the cells in the basic suspension. Most of the mutants showed a requirement for amino acids and vitamins and no base requiring mutants were detected. Based on the frequency of spontaneous reversion, it was found that 9 mutants could be used for further genetic studies, which included the phenotypes: leucine^?, folic acid^?, nicotinic acid^? and inositol^?.     

Leaf physiology variations are modulated by natural variations that underlie stomatal morphology in Populus

Stomata are essential for photosynthesis and abiotic stress tolerance. Here, we used multiomics approaches to dissect the genetic architecture and adaptive mechanisms that underlie stomatal morphology in Populus tomentosa juvenile natural population (303 accessions). We detected 46 candidate genes and 15 epistatic gene-pairs, associated with 5 stomatal morphologies and 18 leaf development and photosynthesis traits, through genome-wide association studies. Expression quantitative trait locus mapping revealed that stomata-associated gene loci were significantly associated with the expression of leaf-related genes; selective sweep analysis uncovered significant differentiation in the allele frequencies of genes that underlie stomatal variations. An allelic regulatory network operating under drought stress and adequate precipitation conditions, with three key regulators (DUF538, TRA2 and AbFH2) and eight interacting genes, was identified that might regulate leaf physiology via modulation of stomatal shape and density. Validation of candidate gene variations in drought-tolerant and F₁ hybrid populations of P. tomentosa showed that the DUF538, TRA2 and AbFH2 loci cause functional stabilisation of spatiotemporal regulatory, whose favourable alleles can be faithfully transmitted to offspring. This study provides insights concerning leaf physiology and stress tolerance via the regulation of stomatal determination in perennial plants.     

Canine postradiation plasma glucose variations

One of the observations of endotoxic or septic shock in canines is the report of concurrent hypoglycemia. Canines exposed to supralethal gamma radiation also develop acute systemic hypotension. This study was performed in order to determine if hypoglycemia develops in the canine concurrent with radiation-induced hypotension. Systemic arterial mean blood pressure (MBP) was measured via femoral arterial catheter. Blood for plasma glucose determinations was obtained from the systemic arterial circulation at the level of the abdominal aorta and from the hepatic portal vein. Plasma glucose levels were determined on a Beckman Glucose Analyzer which employs the enzymatic reaction of β-D-glucose and oxygen. Glucose levels and MBP were monitored for one hour before and for one hour after exposure to 100 Gy, whole-body, gamma radiation or sham radiation for the control animals. Concurrent with postradiation hypotension, we measured a significant decrease in plasma glucose levels in both the systemic arterial circulation and in the hepatic portal vein. Arterial glucose levels in the sham radiated animals showed a slight rise two minutes after sham radiation, falling back to pretreatment, base line levels four minutes later and remaining at that level for the remainder of the hour. Arterial levels in the radiated animals showed a sharp decline two minutes postradiation, falling even further to twenty percent below preradiation levels by one hour postradiation. Venous blood glucose levels in sham radiated animals showed an initial increase and a gradual decrease to five percent below pretreatment base line levels; while glucose levels in radiated animals showed an immediate postradiation decrease continuing to twenty percent below preradiation levels by one hour postradiation. These findings suggest impaired hepatic gluconeogenesis, resulting in postradiation hypoglycemia.