PARTIAL CHARACTERIZATION OF THE NICOTIANA-TABACUM ACTIN GENE FAMILY - EVIDENCE FOR POLLEN-SPECIFIC EXPRESSION OF ONE OF THE GENE FAMILY MEMBERS

The actin gene family of Nicotiana tabacum has been partially characterised by Southern hybridisation and by isolating lambdaEMBL4 recombinants from a genomic library having homology to the soybean actin gene, Sac3. The number of actin genes with homology to Sac3 is estimated at between 20 to 30, based on Southern hybridisation and library screening, though the total gene family may be larger. Twenty-four recombinant lambda clones were isolated, 18 had unique restriction profiles and from these, 2 clones, Tac9 and Tac25, were selected for further study. The region of Tac25 hybridizing to Sac3 was sequenced and shown to contain an open reading frame (ORF) with homology to actin. Partial sequencing of Tac9 revealed a sequence with homology to the third exon of Tac25 and Sac3. The two tobacco actin sequences were compared to other reported actin gene sequences; Tac25 was closely related to the allelic potato actins, Pac58 and Pac85, while Tac9 was more related to Pac79 than to other plant actins. Northern hybridisation analysis showed that while Tac9 detected actin transcripts in RNA from root, leaf, stigma and pollen, Tac25 transcripts were only detected in pollen RNA.