Genetic Map of the tyrT Region of Escherichia coli from 27.1 to 27.7 Minutes Based Exclusively on Sequence Data

The tyrT operon is located at 27 min on the genetic map of the Escherichia coli chromosome (1). The tyrT operon encodes the tRNATYr isoacceptor and is characterized by its unusual structural arrangement consisting of repeated sequence ele-ments. The terminal repeats code for an additional RNA product (4). A genetic map of the tyrT region was generated to charac-terize tyrT deletion mutants and to perform genetic comple-mentation studies. A map of that region has already been described by Leonardo and Clark (12). The map presented here (Fig. 1 and Table 1) is based exclusively on sequence information. It extends the previous map, corrects the orien-tations of genes tyrT and hns, describes the reading frame encoding galU, determines the location of tdk, and closes the gap between tyrT and hns. were completely identical with those previously described (12) but again are shown here to form a contiguous map (Fig. 1 and Table 1). The sequencing and characterization of the genes adjacent to the tyrT promoter region have been described recently (5). The tyrT 5 ' region contained the following genes (5): (i) tgs, which codes for a 32-kDa protein with significant homology to glycinamide ribonucleotide transformylases; (ii) ORF34, show-ing no significant homology to known proteins; and (iii) ORF37, a member of the regulator response protein family. Two further peptides with molecular masses of 34 and 16 kDa were expressed when a plasmid with a 6-kb EcoRI fragment of the tyrT 5 ' region was used in a coupled in vitro transcription-translation assay (5). To determine the sequences of the genes coding for the 34-27.15 min 1289.6 k