SUMMARY This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715–1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.

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-We report the isolation of a mutant of E. coli in which the capacity to synthesize RNA polymerase (EC 2.7.7.6) (the # and ,j' subunits) is rapidly lost at 43'.The mutation has no effect on the stability or activity of the polymerase itself. The mutation is recessive and is closely linked to the rif locus (the structural gene for the ft subunit). Using strains carrying the mutation, we have shown that polymerase is present in excess in rapidly growing E. coli cells.In the Escherichia coli cell one enzyme, RNA polymerase (EC 2.7.7.6; nucleosidetriphosphate:RNA nucleotidyltransferase), carries out all of the synthesis of RNA from DNA templates (1-4). The intracellular concentration of active RNA polymerase molecules directly affects the rate of cell RNA and protein synthesis (5). The concentration of active enzyme is therefore potentially a critical element in determining the rate of cell growth and replication. The enzyme is composed of four subunits (a2pp') (6). The synthesis of the ,B and #' subunits has been observed to be coordinately regulated (5, 7-11), which is consistent with the conclusion that these two subunits are encoded in an operon (12,13). Nothing is known at present about the regulation or genetics of the a subunits. Gene dosage appears to have little effect on the rate of synthesis or final concentration of the enzyme (9, 13-16), suggesting a transcriptional mechanism of regulation. On the other hand, Hayward, Austin, and Scaife (16) have suggested that the regulation of the concentration of RNA polymerase may be post-translational and carried out by the degradation of uncomplexed subunits. The minimum concentration of active RNA polymerase also appears to be regulated, suggesting a mechanism that maintains the intracellular concentration of polymerase at a constant concentration (5). The intracellular concentration of active RNA polymerase molecules is also relatively unaffected by the cell growth rate (9-11), with the enzyme apparently in excess under all growth conditions (9-11).We have begun to investigate the cellular mechanism(s) MATERIALS AND METHODSBacterial Strains. All bacteria were derivatives of E. coli K-12.-They were MX245 (F-, trp, galK, galE, ara, lac, tsx, str, sup), MX390 (F-, leu, argH, trp, galK, galE, lacZ, tsx, str, sup), MX386 (F-, leu, metB, trp, galK, galE, lacZ, tsz, str, sup), MX387 (F-, let, metB, trp, galK, galE, lacZ, tax, str), and MX504 (F-, ppc, pur, trp, galK, galE, lacZ, tsx, str, sup). These five strains were constructed in our laboratory and were derivatives of M238, which was kindly provided by John Abelson. F110/KL131 (F'metB+/ metB-, aroB, argG, leu, recA) and MX255 (metB, aroB, argG, les, recA, val) were constructed from strains obtained from K. B. Low. The Hfr strains used in the mapping were those described by K. B. Low (17) and were kindly provided by him.Media, Chemicals, and Isotopes. R broth (18) was used as the standard medium. Medium E (19) was used to score recombinants in the P1 crosses. When required, the medium was supplemented wit...

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Plant cell nuclei were compared with chicken erythrocyte nuclei for use as internal standards for microspectrophotometry. The amount of DNA per nucleus and the coefficient of variation for measurement of individual nuclei were determined for cells from dormant embryos of Pinus taeda and Pinus coulteri, from onion root tips and from chicken erythrocytes. The chicken erythrocytes had the least variability and thus were best suited for use as a standard. Onion root tips were least suitable, with a coefficient of variation 2 1/2 times that of erythrocytes. Although onion root tips have been used as an internal standard in other studies, their mitotic activity, in contrast with the nonreplication of DNA of mature erythrocytes, is reflected in a broad distribution of nuclei with values in the 2C-4C range. Coulter pine mature embryos were at the 3C level, whether dry or hydrated, while loblolly pine embryos were in the 2C state. This confirms previous reports. The coefficient of variability for the pine embryo cells was 1 1/2 times that of erythrocytes for nonhydrated seeds and twice the erythrocyte value for hydrated seeds. The larger 2C values for pine (26 pg for P. taeda and 17 pg for P. coulteri) are closer to values expected for many plant species than the 3 pg level of the chicken erythrocytes. Dormant P. taeda embryo cells (2C) are suggested as an alternative where the experimental material has large DNA values and/or chicken erythrocytes are difficult to procure. Large sample size is recommended for the plant materials if they are to be used as internal standards in Feulgen cytophotometry.