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A study was described to characterize the Bacillus subtilis gene for phosphatidylserine decarboxylase, psd, and its translation product. The findings indicate that the complete absence of phosphatidylethanolamine in the B subtilis membrane may be offset by the increases in the contents of glucosyldiacylglycerols by an unknown mechanism. Moreover, the results show that both gram-negative and -positive bacteria adopt the de novo phosphatidylserine pathway to form phosphatidylethanolamine.

Escherichia coli strains with pgsA3 mutations exhibited reduced levels of OmpF porin proteins and increased the activation of micF transcription. Reduction in OmpF levels was caused by the acidic-phospholipid deficiency which abolished the flagellation of the mutant cells. The repression of pgsA3 also increased zwitterionic phosphatidylethanolamine levels and reduced acidic phospholipid levels thereby promoting alterations in the gene expression of micF.

Complementation of the temperature sensitivity of an Escherichia coli pssA1 mutant enables the cloning of the Bacillus subtilis pss gene, which encodes phosphatidylserine synthase. This gene encodes a polypeptide of 177 amino acid residues, as indicated by nucleotide sequencing. The regulation of the phospholipid polar head group is affected by the cytoplasmic location of E. coli. Comparative studies of B. subtilis pss and the E. coli counterpart indicate a 35% similarity in the amino acid sequence.

Analysis of pgsA mutants of different phenotypes of E. coli pgsA gene, involved in acidic phospholipid biosynthesis, reveal that pgsA3, pgsA36 and pgsA10 have single-base replacements in codons 60. pgsA3, the most powerful mutant to C in place of wild type 259-A, changing amino acid residue 60 from Thr to Pro. pgA36 mutation has an alteration initiation codon of AUG to AUA and pgs A10 changes amino acid residue 92 from Thr to Ile.