Nucleotide Sequence ofRhizobium meliloti1021 Nodulation Genes:nodDIs Read Divergently fromnodABC

Abstract

Nodulation (nod) genes are required for R. meliloti to invade and stimulate nodule formation in its host, alfalfa. The DNA sequence of nodD, nodA and nodB, which are part of a gene cluster located 20 kb [kilobase] downstream of nifHDK on the R. meliloti pSym megaplasmid was determined. The nodD open reading frame (308 amino acids [aa]) reads from proximal to nifHDK toward distal to nifHDK, divergently from nodA (196 aa) and nodB (217 aa). These 2 genes read from distal to nifHDK toward proximal and are just upstream from the previously defined open reading frame for nodC. Fourteen Tn5 insertion sites were sequenced in nodD, nodA and nodB, revealing no major hotspots for insertion, but an overall preference for G/C bases at positions 1 and 9 of the 9-bp [base pair] repeat.