A cluster of four genes encoding enzymes for five steps in the folate biosynthetic pathway of Streptococcus pneumoniae

Abstract

Two genes, sulB and sulC, in a folate biosynthetic gene cluster of Streptococcus pneumoniae were identified after determination of the DNA sequence between two previously reported genes, sulA and sulD, in a cloned segment of chromosomal DNA containing a mutation to sulfonamide resistance. The gene products, SulB and SulC, correspond to polypeptides of 49 and 21 kDa, respectively. SulC has GTP cyclohydrolase activity and catalyzes the first step in the folate biosynthetic pathway. SulB apparently has dihydrofolate synthetase activity in that it complements a folC mutant of Escherichia coli and thus catalyzes the last step in the pathway. Prior work showed that SulA, a dihydropteroate synthase, and SulD, a bifunctional enzyme, catalyze three intervening steps. Mapping of the mRNA transcribed from the operon was consistent with its beginning at a promoter with a ؊35 site (gTGtCc) and an extended ؊10 site (T-TG-TAaAAT) and its termination at the end of a hairpin structure, which would give a transcript 3,745 nucleotides in length. SulC showed a considerable conservation of sequence by comparison with proven or putative GTP cyclohydrolases from four unrelated species, with 38 to 53% of the residues being identical. A similar comparison of SulB with dihydrofolate synthetases showed an identity of only 26 to 37%. Overall, comparisons of the five folate biosynthetic enzymes in different species suggest that S. pneumoniae is related more closely to other gram-positive bacteria, less closely to eucaryotes, and least closely to the gram-negative E. coli. The varied arrangements of folate biosynthetic genes in different species imply an early evolutionary period of fluidity in genomic rearrangement.

The rnhB gene encoding RNase HII of Streptococcus pneumoniae and evidence of conserved motifs in eucaryotic genes

“…Although its counterpart in C. elegans appears to be a domain in a much larger protein, this may be an anomaly of that invertebrate species. A similar case was observed in the folate biosynthetic system, present in Pneumocystis carinii, where four domains present as single proteins in other species (21) are joined together to make a single polyprotein (42). Accordingly, the polypeptide components of RNase HII in human cells may be similar in size to that in S. pneumoniae.…”

Molecular Analysis of Murine Leukemia Cell Lines Resistant to 5,10-Dideazatetrahydrofolate Identifies Several Amino Acids Critical to the Function of Folylpolyglutamate Synthetase

“…Single nucleotide mutations were found in the expressed coding region of the FPGS gene for cDNA from each mutant cell line (Table III). 50 …”

Activator Role of the Pneumococcal Mga-Like Virulence Transcriptional Regulator

“…To investigate whether Mga Spn influenced the activity of a particular promoter in vivo, we constructed a pneumococcal strain designed to overproduce Mga Spn . First, we constructed the PsulA::mga fusion gene, in which the Pmga promoter of the mga Spn gene was replaced with the promoter of the pneumococcal sulA gene (PsulA) (18,32). The fusion gene was then inserted into pDL287 (21), generating the pDLPsulA::mga recombinant.…”