Genetic analysis of picornaviruses.

During the past year, genetic studies of picornaviruses, vastly facilitated by the application of infectious picornaviral cDNAs and RNAs, have contributed to our understanding of the function of individual picornavirus polypeptides and to the genetic processes that operate in these small RNA viruses. Especially notable were the demonstrations that the RNA-dependent RNA polymerase may have a function in RNA synthesis as an uncleaved precursor polypeptide, and that a mutation in the polymerase can be complemented in trans, in contrast to data obtained from previously studied polymerase mutants. A new in vitro system, in which positive-strand synthesis, negative-strand synthesis and RNA packaging were all observed, will facilitate further studies into the mechanism of these processes.     

Genetic toxicology of bleomycin.

Bleomycin (BLM), an antibiotic obtained from Streptomyces verticillus, is of significance as an antineoplastic agent. The compound is actually the mixture of some 200 related forms which differ from each other in the amine moiety. The drug, at low concentrations, can cause elimination of bases, particularly thymine. This causes strand breakage of DNA and inhibition of cell growth. The influence of BLM on cell growth may be unrelated to the effects on DNA. In general, mitotically dividing cells show more DNA damage than non-dividing cells. G2 seems to be the most sensitive phase indicating that cell death may not be related to a direct effect of BLM on DNA replication. The antibiotic shows specific effects on chromatin and causes chromosomal damage in all sub-phases of interphase. It can affect early prophase chromosomes also. Suggestion has been made that BLM-induced breakage and cell death are similar to those induced by densely ionizing radiations. Whereas the antibiotic affects the frequency of somatic crossing over and produces micronuclei, the data on mutation induction and production of sister-chromatid exchanges do not permit classifying BLM as a potent inducer of these phenomena. The genetic effects of BLM can be modified quantitatively by thiol compounds, caffeine, hyperthermia and H2O2. It is concluded that the available data do not permit assessment of genetic damage in the offsprings of BLM-treated patients. Such studies are urgently needed, as are the studies to find out the effects of BLM on meiotic phenomena.     

Genetic effects of hydralazine.

Hydralazine and its acetone condensation product (ACP) were found to induce base-pair substitution mutations in the Salmonella/microsomal activation test system and to display genetic toxicity in the PolA+/A- test system. Incubation with a rat-liver microsomal fraction did not affect the genetic toxicity of either compound. Other derivatives of hydralazine, including the major metabolite, 3-hydroxy-methyl-s-triazolo-[3,4a]phthalazine, did not yield any evidence of genetic toxicity nor were they metabolically convertible to a toxic product. Therefore, individuals who convert hydralazine to MTP slowly, the "slow acetylators", would be expected to be at risk.     

Genetic manipulation of kinetoplastida.

During the 1980s, many kinetoplastid genes were cloned and their function inferred from homology with genes from other organisms, location of the corresponding proteins or expression in heterologous systems. Up until 1990, before the availability of DNA transfection methodology, we could not analyze the function of kinetoplastid genes within the organisms themselves. Since then, it has become possible to create and complement mutants, to overexpress foreign proteins in the parasites, to knock out genes and even to switch off essential functions. However, these methods are not equally applicable in all parasites. Here, Christine Clayton highlights the differences and similarities between the most commonly used model organisms, and assesses the relative advantages of different approaches and parasites for different types of investigation.     

Genetic marker technology.

Advances in our understanding of polymorphisms found in eukaryotic genomes and improved methods for studying genetic markers should facilitate genetic linkage mapping and other applications. Progress within the past year includes characterization of the types, frequencies, and properties of tandemly repeated sequences, methods for obtaining the DNA sequence flanking genetic markers for use in the polymerase chain reaction, and new detection systems featuring automation and multiplexing.