The major chlorophyll a/b binding protein of petunia is composed of several polypeptides encoded by a number of distinct nuclear genes.

Five distinct cDNA clones for the major chlorophyll a/b binding protein (Cab) of the petunia thylakoid membrane light-harvesting complex have been characterized. The nucleotide sequences of the polypeptide coding regions are similar between clones; however, the 3'-untranslated regions are divergent. Analysis of petunia nuclear DNA through genomic hybridizations and characterization of cloned nuclear fragments indicates there are at least sixteen genes for the major Cab protein. These genes can be classified into at least five small multigene families on the basis of their homology to the different cDNA clones. Two families contain only two genes each and in both cases the genes are closely linked in the genome. In one case, one gene is in an inverted orientation with respect to the other such that the 5' ends are adjacent; in the other case, the two genes are in a tandem array. Both genes from one of these families are transcribed in green leaves. The genes belonging to separate nuclear gene families encode different polypeptide components of the major Cab protein.