Mice in tumor susceptibility studies were monitored daily

isolates are indeed cysB-lac+ fusion which cysB + was introduced indicates some sort of regulation of cysB gene expression. It seems possible that the cysB protein regulates expression of its own structural gene to avoid overproduction. Another explanation requires the existence of another gene regulated by cysB, whose product directly or indirectly controls cysB gene expression. Many attempts PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19820119 to isolate additional elements regulatory for the cysteine biosynthetic pathway have been undertaken but thus far have produced no positive results. In some cysB-lac+ fusion strains introduction of a cysB + allele did not decrease f,-galactosidase levels. These fusion strains may carry unknown regulatory mutations which have been selected for during the period of incubation necessary to obtain the Lac’ clones. If these strains do carry mutations which render cysB insensitive to autoregulation, they may prove useful in the isolation of strains order AVE8062A producing large amounts of cysB protein. These fusion strains are under investigation. ~~