A form of the human skin disease, ichthyosis, results from a mutation at the steroid sulphatase locus (STS) on the X chromosome. This locus appears to escape inactivation in the XX female, resulting in the expression of two doses of the STS gene (Shapiro et al. 1978; Crawfurd, 1982). The scurfy mutation in the mouse is thought to be homologous to the human disease (McKusick, 1978), and so should also be due to a steroid sulphatase (STS) deficiency. Our findings in male and female mice suggest that, in contrast to the human, the murine ‘STS’ locus is subject to X chromosome inactivation. However, another interpretation of the results is possible, namely that STS may be coded for by an autosomal gene.

This report describes the existence of a mutation in a proA1 pabaA6 yA2 strain of Aspergillus nidulans, which prevents it growing on elevated concentrations of nitrite. The nitrite toxicity marker (nihA) resulted from a mutation in a single gene representing a new locus in linkage group I, and behaved as a recessive character. The observed recombination frequencies between nihA and proA1 and between nihA and pabaA6 were about 1 and 11%, respectively. Nitrite toxicity was not due to a defect in nitrite reductase, because the mutant grew well on nitrate. Furthermore, ammonium protected both nis-5 and niiA− strains against nitrite toxicity, which was not observed for the nihA strain. Since growth of the mutant was inhibited more by a mixture of ammonium and nitrite, compared to nitrite alone, it is proposed that the proA1 pabaA6 yA2 strain has a mutation leading to increased efficiency in nitrite uptake, which is not repressed by ammonium.

RP4::Mu was used to insert Tn3171 into the Acinetobacter calcoaceticus EBF65/65 chromosome. Insertions occurred at a frequency of approximately 10−7 per recipient cell. Auxotrophic mutations resulted from 28% of the Tn3171 insertions examined, with a possible ‘hot-spot’ for insertion in a gene for arginine biosynthesis. The frequency of subsequent precise excision of Tn3171 from the chromosome was less than 10−10. When attempts were made using RP4 derivatives to mobilize the chromosome from a strain containing an arg::Tn3171 insertion, it was found that the enhanced transfer frequency of the adjacent region of the chromosome was dependent on the original Tn3171 insertion, but was independent of the presence of Tn3171 on the mobilizing plasmid.

Genet. Res., Camb. (1982), 39, pp. 157–168

The relationship between heterochromatic homology and meiotic segregation of compound second autosomes during spermatogenesis in Drosophila melanogaster

By Arthur J. Hilliker, David G. Holm and R. Appels

Several errors occurred in the headings of Table 4, on p. 162: the table should read as follows:

Structural genes for the isozymes of shikimate dehydrogenase (E.C. 1.1.1.25) have been located on chromosome arms 5AS, 5BS and 5DS of wheat, 5RS of cereal rye and on chromosome 5Cu of Aegilops umbellulata by electrophoretic techniques. This character provides a useful genetic marker for these previously unmarked chromosome arms, and the results support the notion of the conservation of gene synteny groups within the Triticinae.