Expression and genomic organization of a dinoflagellate gene family

The luciferin-binding protein (LBP) of the dinoflagellate Gonyaulax polyedra is encoded by a large gene family with at least two different members. To more fully understand the expression and genomic organization of this gene family, 40 full-length LBP cDNAs were isolated and mapped with the restriction enzymes Xho I, Eco RI, Pvu II and Hind III. All cDNAs isolated could be placed into one of two groups called LBP alpha and LBP beta. Two LBP alpha group cDNAs were completely sequenced and were found to share 99% identity at both the nucleotide and protein levels. One LBP beta cDNA was sequenced and was found to share only 86% sequence identity with the LBP alpha group at both the nucleotide and protein levels. Both groups of message appear to be expressed at nearly equal levels since (1) two-dimensional gels of purified LBP show two protein isoforms present in roughly equal amounts and (2) northern blots using group-specific probes suggest that cellular levels of LBP alpha and LBP beta mRNAs are identical. Genomic Southern blots using group-specific probes suggests that the copy number of both gene groups is very similar and that LBP gene loci are organized as tandem repeats of either LBP alpha or LBP beta sequences.