title: The gene for the longest known Escherichia coli protein is a member of helicase superfamily II.
abstract: The Escherichia coli rnt gene, which encodes the RNA-processing enzyme RNase T, is cotranscribed with a downstream gene. Complete sequencing of this gene indicates that its coding region encompasses 1,538 amino acids, making it the longest known protein in E. coli. The gene (tentatively termed lhr for long helicase related) contains the seven conserved motifs of the DNA and RNA helicase superfamily II. An approximately 170-kDa protein is observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 35S-labeled extracts prepared from cells in which lhr is under the control of an induced T7 promoter. This protein is absent when lhr is interrupted or when no plasmid is present. Downstream of lhr is the C-terminal region of a convergent gene with homology to glutaredoxin. Interruptions of chromosomal lhr at two different positions within the gene do not affect the growth of E. coli at various temperatures in rich or minimal medium, indicating that lhr is not essential for usual laboratory growth. lhr interruption also has no effect on anaerobic growth. In addition, cells lacking Lhr recover normally from starvation, plate phage normally, and display normal sensitivities to UV irradiation and H2O2. Southern analysis showed that no other gene closely related to lhr is present on the E. coli chromosome. These data expand the known size range of E. coli proteins and suggest that very large helicases are present in this organism.
authors.affiliation: Department of Biochemistry, University of Connecticut Health Center, Farmington 06032, USA.
authors.forename: N B
authors.initials: NB
authors.lastname: Reuven
authors.forename: E V
authors.initials: EV
authors.lastname: Koonin
authors.forename: K E
authors.initials: KE
authors.lastname: Rudd
authors.forename: M P
authors.initials: MP
authors.lastname: Deutscher
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D017124:Conserved Sequence / Q000235:genetics; D004265:DNA Helicases / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D029968:Escherichia coli Proteins; D005095:Exoribonucleases / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation; D015183:Restriction Mapping; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D005095:Exoribonucleases; C042081:exoribonuclease T; D004265:DNA Helicases; C095870:Lhr protein, E coli