CLOSE LINKAGE OF GENES ENCODING GLUTAMINE SYNTHETASE-I AND SYNTHETASE-II IN FRANKIA-ALNI CPI1

Frankia alni CpI1 has two glutamine synthetases (GSs), GSI and GSII. T he GSI gene (glnA) was isolated from a cosmid library of F. alni CpI1 DNA by heterologous probing with glnA from Streptomyces coelicolor. Th e glnA gene was shown to be located upstream of the GSII gene (glnII) by DNA-DNA hybridization. The nucleotide sequences of the 1,422-bp CpI 1 glnA gene and of the 449-bp intervening region between glnA and glnI I were determined, and the glnA amino acid sequence was deduced. In co mmon with GSIs from other organisms, CpI1 GSI contains five conserved regions near the active site and a conserved tyrosine at the adenylyla tion site. F. alni CpI1 glnA complemented the glutamine growth require ment of the Escherichia coli glnA deletion strain YMC11 but only when expressed from an E. coli lac promoter. While the functional significa nce of maintaining two GSs adjacent to one another remains unclear, th is arrangement in F. alni provides support for the recently proposed o rigin of GSI and GSII as resulting from a gene duplication early in th e evolution of life.