The enzyme chorismate synthase was purified in milligram quantities from an overproducing strain of Escherichia coli. The amino acid sequence was deduced from the nucleotide sequence of the aroC gene and confirmed by determining the N-terminal amino acid sequence of the purified enzyme. The complete polypeptide chain consists of 357 amino acid residues and has a calculated subunit Mr of 38,183. Cross-linking and gel-filtration experiments show that the enzyme is tetrameric. An improved purification of chorismate synthase from Neurospora crassa is also described. Cross-linking and gel-filtration experiments on the N. crassa enzyme show that it is also tetrameric with a subunit Mr of 50,000. It is proposed that the subunits of the N. crassa enzyme are larger because they contain a diaphorase domain that is absent from the E. coli enzyme.

SUMMARYAn investigation was undertaken to determine the isolation rate and antibiotic resistance ofHaemophilus influenzae from the nasopharynx of young children. The 996 subjects studied were up to 6 years of age. H. influenzae was isolated from 304 (30 5 %) and strains of capsular type b from 11 (1 1 %). Age, sibling status, season, respiratory infection and antibiotic therapy all influenced isolation rates. The overall prevalence of antibiotic resistance in the strains isolated was ampicillin 5-4% (all fl-lactamase producers), cefaclor 0-3 %, chloramphenicol 1-3%, erythromycin 38-2 %, tetracycline 1 3 %, trimethoprim 5-4 % and sulphamethoxazole 0%. Ampicillin resistance was more common in type b than non-capsulated strains.

The aroL gene encoding the enzyme shikimate kinase II was cloned from Escherichia coli K12. Construction of over-expressing strains permitted for the first time the purification to homogeneity of a monofunctional shikimate kinase. The complete amino acid sequence of shikimate kinase II was determined by a combined nucleotide and direct amino acid sequencing strategy. E. coli shikimate kinase II is a monomeric enzyme containing 173 amino acid residues with a calculated Mr 18 937. The amino acid sequence contains a region homologous with other kinases and ATP-requiring enzymes. Evidence is presented suggesting that the transcriptional start site of the aroL gene is located within a potential operator site.

The complete amino acid sequence of the Escherichia coli 3-dehydroquinate synthase has been determined by a combined nucleotide and direct amino acid sequencing strategy. E. coli 3-dehydroquinate synthase is 362 amino acids long and has a calculated Mr of 38 880. Analysis of the aroB nucleotide sequence and its 5'- and 3'-flanking regions has identified the aroB promoter elements and a possible 3'-terminator site.

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