Genetic analysis of a chromosomal region containing genes required for assimilation of allantoin nitrogen and linked glyoxylate metabolism in Escherichia coli

Growth experiments with Escherichia coli have shown that this organism is a ble to use allantoin as a sole nitrogen source but not as a sole carbon sou rce. Nitrogen assimilation from this compound was possible only under anaer obic conditions, in which all the enzyme activities involved in allantoin m etabolism were detected. Of the nine genes encoding proteins required for a llantoin degradation, only the one encoding glyoxylate carboligase (gcl), t he first enzyme of the pathway leading to glycerate, had been identified an d mapped at centisome 12 on the chromosome map. Phenotypic complementation of mutations in the other two genes of the glycerate pathway, encoding tart ronic semialdehyde reductase (glxR) and glycerate kinase (glxK), allowed us to clone and map them closely linked to gel, Complete sequencing of a 15,8 -kb fragment encompassing these genes defined a regulon with 12 open readin g frames (ORFs), Due to the high similarity of the products of two of these ORFs with yeast allantoinase and yeast allantoate amidohydrolase, a system atic analysis of the gene cluster was undertaken to identify genes involved in allantoin utilization. A BLASTP search predicted four of the genes that we sequenced to encode allantoinase (allB), allantoate amidohydrolase (all C), ureidoglycolate hydrolase (allA), and ureidoglycolate dehydrogenase (al lD), The products of these genes were overexpressed and shown to have the p redicted corresponding enzyme activities. Transcriptional fusions to lacZ p ermitted the identification of three functional promoters corresponding to three transcriptional units for the structural genes and another promoter f or the regulatory gene allR, Deletion of this regulatory gene led to consti tutive expression of the regulon, indicating a negatively acting function.