Mutational specificity and the influence of excision repair: insights into the mechanisms of error-avoidance and error-fixation

The excision repair process controlled by the uvrABC gene in Escherichia coli is the major pathway for the repair of a diverse series of DNA damages. To achieve a better understanding of the mechanics of this repair pathway and its impact upon mutagenesis, we have applied a recently developed technology by which the nature of mutation is determined at the DNA sequence level. A comparison of the classes and distribution of mutation in excision-repair-proficient and excision-repair-deficient strains of E. coli reveals that the absence of excision repair can alter both the nature of the mutations recovered as well as their distribution. This can occur in one of several ways. For example, under some circumstances the action of the UvrABC pathway can lead to interruptions of DNA strand continuity and an enhancement of both frameshift and deletion events. Such an effect is seen following damage by psoralen plus near UV (PUVA) treatment that produces crosslinks in the DNA. In comparison, several other treatments produce similar distributions within the classes of mutations recovered but demonstrate an alteration in site specificity. Such is the case following UV irradiation. In this case, the data indicate that while the premutagenic lesions may be the same, mutation fixation in the presence and absence of excision repair may involve different mechanisms. Similarly, evidence from the repair of damage by ethylating agents indicates that while the nature of the mutations recovered is not altered, the preferred location of these events is altered in the absence of excision repair. These results indicate that local DNA sequence can affect on the efficiency of excision repair.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypermodified nucleoside carboxyl group as a target site for specific tRNA modification

The free carboxyl group of hypermodified nucleosides N6-methyl-N6-(threoninocarbonyl)adenosine (mt6A37) and 3-(3-amino-3-carboxypropyl)uridine (acp3U20:1) in tRNAmMet (yellow lupine), and N6-(threoninocarbonyl)adenosine (t6A37) in tRNAiMet (yellow lupine) can be converted quantitatively and under very mild conditions into the respective anilides in a reaction with aniline and a water-soluble carbodiimide. The tRNA reactions proceed with rates very similar to that reported previously for t6A nucleoside. Detailed analysis of the products of tRNA modification with [3H]aniline on tRNA (chromatography on BD-DEAE-cellulose), oligonucleotide (polyacrylamide gel electrophoresis) and nucleoside (HPLC on Aminex A6) levels clearly indicates that only the hypermodified nucleoside residues undergo the reaction. The site of modification is confirmed for mono-modified (at mt6A37) and bis-modified (at mt6A37 and acp3U20:1) tRNAmMet, and for mono-modified (at t6A37) tRNAiMet by sequence analysis using 5'end 32P-labeled tRNAs. The modification procedure seems to be universally applicable for all hypermodified nucleosides bearing a free carboxyl group and for different amine reagents designed for the studies on tRNA function.     

Positive anemotaxis by Varroa mites: responses to bee odour plumes and single clean‐air puffs

Abstract.The stimuli and mechanisms mediating host location and host choice by the bee mite, Varroa jacobsoni (Oudemans), are currently unknown. It is shown that Varroa can use single clean‐air puffs and bee‐odour plumes in a wind tunnel as directional cues. Varroa turned nearly straight upwind in response to single 0.1‐s puffs of clean air directed at 90° to the their anterior‐posterior axis. They turned significantly further to their left side (104°) than to their right (76°), but showed no difference in latency to initiation of the turns (means of 63.3 ms vs. 62.6 ms, respectively). They also followed bee‐odour plumes in a wind tunnel. When released in odour and control plumes mid‐way between the plume's origin and the downwind end of the tunnel, mites responding to bee‐odour walked upwind in, or along the edge of, the odour plume with 38% making contact with the odour delivery tube; mites in clean air did not walk upwind along the air stream, and none made contact with the air delivery tube. Walking speeds were not different between the bee‐odour and control groups (0.28 vs. 0.29 cm s^–1); there were also no differences in the turning rates (96.85 vs. 97.16 deg s^–1 and 388.08 vs. 379.18 deg cm^–1, respectively). Under all conditions, mites walked in a zigzag fashion.     

On the synonymy and distribution of the heteropterans, Trapezonotus dispar Stål and T. desertus Seidenstücker (Heteroptera, Lygaeidae)

Trapezonotus dispar Stål, 1872 is subdivided into two subspecies, T. dispar dispar (Europe) and T. dispar breviceps Jakovlev, 1882 (= T. seductor Horváth, 1883) (Caucasus and Asia Minor). T. inglorius Vinokurov, 1990 is synonymized with T. desertus Sedienstücker, 1951.     

Microsatellite markers for the common bean Phaseolus vulgaris

Efforts to develop molecular tools for genetic analysis and breeding of common bean in the tropics are still limited. The number of microsatellite markers available for the crop is small compared to other crops of similar social and economic importance. As part of a project to broaden the use of molecular tools in bean breeding, a genomic library enriched for AG/TC repeat sequences was constructed for Phaseolus vulgaris. Twenty microsatellite markers were initially developed and 10 were characterized using a panel of 85 representative accessions of the bean gene bank. The number of alleles per marker ranged from three to 10. The polymorphism information content (PIC) varied from 0.23 to 0.80. The results indicate that the new markers can be readily used in genetically analysis of common bean.