DETERMINATION OF STEADY-STATE MESSENGER-RNA LEVELS OF INDIVIDUAL CHLOROPHYLL A/B BINDING-PROTEIN GENES OF THE TOMATO CAB GENE FAMILY

The steady-state levels of mRNA produced by 14 genes encoding members of the tomato chlorophyll a/b binding protein family were quantified. All genes were found to be expressed in leaf tissue, but the mRNAs accumulated to significantly different levels. The transcripts of cab 1 A, cab 1 B, cab 3 A and cab 3 B, encoding the Type I LHC proteins of photosystem II, are abundant, while low levels were measured for mRNAs encoding the Type II LHC II and the LHC I proteins. Sequences from the 5' upstream regions (400 to translational start) of some cab genes were determined in this study, and a total of 16 tomato cab gene promoters for which sequences are now available were analyzed. Significant sequence conservation was found for those genes which are tandemly linked on the chromosome. However, the level of sequence conservation is different for the different cab subfamilies, e.g. 85% similarity between cab 1 A and cab 1 D vs. 45% sequence similarity between cab 3 A and cab 3 C upstream sequences. Characteristic GATA repeats with a conserved spacing were found in 5' upstream sequences of cab 1 A-D, cab 3 A-C, cab 11 and cab 12. The consensus sequence CCTTATCAT, which is believed to mediate light responsiveness, was found at different locations in the upstream sequences of cab 6 B, cab 7, cab 8. cab 9. cab 10A, cab 10B and cab 11. In 11 out of 15 genes the transcription initiation site was found to center on the triplet TCA.