Intracellular lytic enzyme systems and their use for disruption of Escherichia coli.

This article focusses on lytic enzyme systems available in E. coli and their potential use for cellular disruption. In the systems described here the genetic information for lysis would be carried within the microbial host, either integrated or naturally occurring on chromosomal DNA, or on extrachromosomal elements such as plasmids. Each microbe would carry complete information for endogenous enzymatic lysis, and lysis would occur in a controlled manner after being triggered by an external factor such as temperature or inducer addition. The lytic systems explored in this review include the autolytic enzymes, colicin lytic enzymes, and bacteriophage lytic enzymes from phage phiX174, T4, lambda, MS2 and Q beta. Many of the colicin lytic enzymes and all of the bacteriophage lytic enzymes described here have been cloned, and in some instances examined as cellular disruption methods. None of the E. coli autolytic enzymes have been cloned, but information pertinent for use as a disruption method is described.

Differential expression of steroid sulphatase locus on active and inactive human X chromosome.

The X chromosome in mammalian somatic cells is subject to unique regulation--usually genes on a single X chromosome are expressed while those on other X chromosomes are inactivated. The X-locus for steroid sulphatase (STS; EC 3.1.6.2), the microsomal enzyme that catalyses the hydrolysis of various 3 beta-hydroxysteroid sulphates, is exceptional because it seems to escape inactivation. Evidence for this comes from fibroblast clones in females heterozygous for mutations that result in a severe deficiency of this enzyme in affected males; all clones from these heterozygotes have STS activity, and enzyme-deficient clones that are expected if the locus were subject to inactivation, have not been found. Further evidence that the STS locus escapes inactivation is that the human inactive X chromosomes contributes STS activity to mouse-human hybrid cells. On the basis of these hybrid studies the STS locus has been mapped to the distal half of the short arm (p22-pter) of the human X chromosome. Although the STS locus on both X chromosomes in human female cells is expressed, quantitative measurements of STS activity in males and females do not accurately reflect the sex differences in number of X chromosomes (Table 1). The ratio of mean values for normal females to that of normal males is greater than 1:1 but less than the ratio of 2:1 expected if STS loci on all X chromosomes were equally expressed. The incomplete dosage effect suggests that the STS locus on the inactive X chromosome might not be fully expressed. To test this hypothesis, we examine two heterozygotes for X-linked STS deficiency who were also heterozygous for the common electrophoretic variants of glucose-6-phosphate dehydrogenase (G6PD A and B). Studies of fibroblast clones from these females provide evidence, presented here, for differential expression of STS loci on the active and inactive X chromosome.