We have characterized the cDNA and genomic sequences that encode actin from the multicellular red alga Chondrus crispus. Southern-blot analysis indicates that the C. crispus actin gene (ChAc) is present as a single copy. Northern analysis shows that, like the GapA gene, the actin gene is well expressed in gametophytes but weakly in protoplasts. Compared to actin genes of animals, fungi, green plants and oomycetes, that of C. crispus displays a higher evolutionary rate and does not show any of the amino-acid signatures characteristic of the other lineages. As previously described for GapA, ChAc is interrupted by a single intron at the beginning of the coding region. The site of initiation of transcription was characterized by RNAse protection. The promoter region displays a CAAT box but lacks a canonical TATA motif. Other noticeable features, such as a high content of pyrimidines as well as a 14-nt motif found in both the 5'-untranslated region and the intron, were observed.
The atpB and the atpE genes encode for the/~ and subunits of the proton-translocation ATPase complex in prokaryotes, mitochondria and chloroplasts. In E. coli and e-purple eubacteria the genes for all subunits of the ATPase complex are linked and constitute a single transcriptional unit [1,2]. In contrast, the cyanobacterial and green plastid atpB and atpE genes form a separate 'atpB' cluster which is encoded by the chloroplastic genome in plants [3,4].Little is known about the organization of AT-Pase genes in brown and red algae. In this report we present the nucleotide sequence of the atpB-atpE region encoded by the chloroplastic genome of the brown alga PylaieIla littoralis (L.) Kjellm (Fig. 1).The 4.2 kb Eco RI chloroplastic DNA fragment E13 of P. littoralis [5] hybridized with a spinach atpB probe [6] and was sequenced in both directions using the dideoxy sequencing method and synthetic oligonucleotides (Eurogentec S.A., Libge, Belgium). This region contains two adjacent open reading frames, which by comparison with other known sequences have been identified as the atpB and atpE genes. Their lengths are 1446 bp (482 codons) and 399 bp (133 codons) respectively. They are separated by a 14 nucleotide spacer region (Fig. 1).Comparisons with homologous genes from prokaryotes and green plastids (Figs. 2 and 3) indicate that the atpB genes are, in all cases, more conserved than the atpE genes. The percentages of identical amino acid residues between the atpB and atpE genes of P. littoralis and those of other species (calculated from the alignments, data not shown) indicate that these genes probably have a cyanobacterial origin as do those of green plastids [5].Because of the similar organisation of this region to that of other plants it appears probable that these genes are also cotranscribed [4]. Figure 4 shows the similarities in the organization of the junction region between the atpB and atpE genes of land plants and P. littoralis. It is noteworthy that the AAATGA sequence, which in land plants comprises the atpB stop codon and the atpE start codon (implying a slide backwards of ribosomes to the -1 frame on mRNA) is exactly conserved at the same position in P. littora-Iis, although the putative atpB stop codon is 12The nucleotide sequence data reported will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases underthe accession number X60329.
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