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In Escherichia coli, the first enzyme of the diaminopimelate and lysine pathway is dihydrodipicolinate synthetase, which is feedback-inhibited by lysine and encoded by the dapA gene. The location of the dapA gene on the bacterial chromosome has been determined accurately with respect to the neighboring purC and dapE genes. The complete nucleotide sequence and the transcriptional start of the dapA gene were determined. The results show that dapA consists of a single cistron encoding a 292-amino acid polypeptide of 31,372 daltons.

A total of 30 cases of 46,XX true hermaphroditism was analysed for Y-DNA sequences including the recently cloned gene for male testis-determination SRY. In 3 cases, a portion of the Y chromosome including SRY was present and, in 2 cases, was localised, to Xp22 by in situ hybridisation. Since previous studies have shown that the majority of XX males are generated by an X-Y chromosomal interchange, the Xp22 position of the Yp material suggests that certain cases of hermaphroditism can arise by the same meiotic event. The phenotype in the 3 SRY-positive cases may be caused by X-inactivation resulting in somatic mosaicism of testis-determining factor expression giving rise to both testicular and ovarian tissues. Autosomal or X-linked mutation(s) elsewhere in the sex-determining pathway may explain the phenotype observed in the remaining 27 SRY-negative cases.

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The regulation of lysA which encodes the last enzyme for lysine biosynthesis in Escherichia coli, diaminopimelic acid-decarboxylase, was studied by using lysA-lacZ fusions. Our results indicate an absolute requirement for the LysR product for its activation, LysR protein present in a limiting amount which can be titrated by a multicopy plasmid carrying its target site and a negative regulatory role for the LysA protein itself which decreases lysA-lacZ expression 30-fold.