Nucleotide sequence of the gene for the M r 32,000 thylakoid membrane protein from Spinacia oleracea and Nicotiana debneyi predicts a totally conserved primary translation product of M r 38,950

Abstract

The gene for the so-called MW 32,000 rapidly labeled photosystem II thylakoid membrane protein (designated psbA) of spinach (S. oleracea) chloroplasts is located on the chloroplast DNA in the large single-copy region immediately adjacent to one of the inverted repeat sequences. The size of the mRNA for this protein is .apprxeq. 1.25 kbase and the direction of transcription is towards the inverted repeat unit. The nucleotide sequence of the gene and its flanking regions is presented. The only large open reading frame in the sequence codes for a protein of MW 38,950. The nucleotide sequence of psbA from N. debneyi was determined, and comparison of the sequences from the 2 spp. shows them to be highly conserved (> 95% homology) throughout the entire reading frame. Conservation of the amino acid sequence is absolute, there being no changes in a total of 353 residues. Apparently, the primary translation product of psbA must be a protein of MW 38,950. The protein is characterized by the complete absence of lysine residues and is relatively rich in hydrophobic amino acids, which tend to be clustered. Transcription of spinach psbA starts about 86 base pairs before the 1st ATG codon. Immediately upstream from this point there is a sequence typical of that found in Escherichia coli promoters. An almost identical sequence occurs in the equivalent region of N. debneyi DNA.