Escherichia coli molecular genetic map (1000 kbp): update I.

The sequenced genes from Escherichia coli that are available in the EMBL library (release 21) have been localized on an updated and corrected version of the restriction map of the chromosome generated by Kohara et al. (1987). One thousand kbp of sequenced DNA are incorporated in this update; this is equivalent to 23% of the total genome. The accuracy of the map is assessed, and it is corrected and updated where appropriate. A significant number of sites were missing from the original map, mainly involving two of the eight enzymes used by Kohara et al. (1987), ie. PvuII and EcoRV. The nucleotide environment of such missing sites was examined and, using an Artificial Intelligence approach, it appears that the site for these enzymes is sensitive to context effects. Several genes of known position on the E. coli chromosome could not be placed on the restriction map; this suggests that additional gaps are likely to exist on the restriction map, in addition to the original seven identified by Kohara et al. We have also obtained information about the probable direction of transcription of chromosomal genes with respect to the map. Most genes are transcribed in the same direction as the replication forks, particularly around oriC at 84 min.