Linkage and homology analysis divides the eight genes for the small subunit of petunia ribulose 1,5-bisphosphate carboxylase into three gene families.

Twenty-six lambda phage clones with homology to coding sequences of the small subunit (SSU) of ribulose 1,5-bisphosphate carboxylase have been isolated from an EMBL3 lambda phage bank of Petunia (Mitchell) DNA. Restriction mapping of the phage inserts shows that the clones were obtained from five nonoverlapping regions of petunia DNA that carry seven SSU genes. Comparison of the HindIII genomic fragments of petunia DNA with the HindIII restriction fragments of the isolated phage indicates that petunia nuclear DNA encodes eight SSU genes, seven of which are present in the phage clones. Two incomplete genes, which contain only the 3' end of an SSU gene, were also found in the phage clones. We demonstrate that the eight SSU genes of petunia can be divided into three gene families based on homology to three petunia cDNA clones. Two gene families contain single SSU genes and the third contains six genes, four of which are closely linked within petunia nuclear DNA.