Isolation, sequence and expression of two members of the 32 kd thylakoid membrane protein gene family from the cyanobacterium Anabaena 7120.

The cyanobacterium Anabaena contains at least three copies of DNA sequences related to the unique gene encoding the 32 kd thylakoid membrane protein in spinach chloroplast DNA, based on hybridization with the cloned spinach probe. Two of the identified Anabaena DNA fragments were isolated from a recombinant lambda library and the complete nucleotide sequences of the coding regions were determined. Both fragments contain open reading frames coding for proteins of MW 39 950. The predicted amino acid sequences are 94% identical; 87% of the positions are identical to those of the corresponding spinach protein. The nucleotide sequences of the 5' and 3' flanking regions of the two Anabaena genes differ considerably. Based on S1 nuclease protection, primer extension, and Northern hybridization experiments it is concluded that only one of the two cloned genes is transcribed in Anabaena cells growing on complete medium (containing ammonia). Under these conditions it appears that none of the other related sequences, not yet cloned, is transcribed. Transcription of only one member of the multigene family provides a possible explanation for the ability to isolate mutants resistant to the herbicide DCMU, whose target is believed to be the 32 kd protein.