The petunia chlorophyll a/b binding protein genes: a comparison of Cab genes from different gene families

Abstract

In Petunia (Mitchell) there are at least 16 genes which encode the chlorophyll a/b binding proteins; these genes have been classified into small multigene families based upon nucleotide sequence homology (1). A gene from each of five distinct Cab gene families is compared here. These genes have uninterrupted open reading frames of 266 or 267 amino acids corresponding to the Cab precursor proteins of sizes around 32000 daltons. A comparison of the amino acid sequences deduced here with published information from direct NH2-terminal analysis of a mature Cab protein in pea (10) suggests that a 34-36 amino acid transit peptide is cleaved from the NH2-terminal of the petunia precursor proteins. The proposed transit peptide sequences are more divergent than the mature peptide sequences between the Cab genes from different gene families. There are two regions within the mature Cab proteins which are conserved between all genes--a sequence of 28 amino acids near the NH2 terminal, and another sequence of 26 amino acids in the middle of the protein. The DNA sequences proximal to the Cab coding regions contain typical eukaryote promoter elements--TATA and CCAAT boxes, and in addition those genes which are known to be expressed in petunia leaf tissue also have an extensive region of homology (48 nucleotides) centered at approximately 130 nucleotides from the proposed transcription start sites.