STRUCTURAL FEATURES AND PHYLOGENY OF THE ACTIN GENE OF CHONDRUS-CRISPUS (GIGARTINALES, RHODOPHYTA)

We have characterized the cDNA and genomic sequences that encode actin from the multicellular red alga Chondrus crispus. Southern-blot analy sis indicates that the C. crispus actin gene (ChAc) is present as a si ngle copy. Northern analysis shows that, like the GapA gene, the actin gene is well expressed in gametophytes but weakly in protoplasts. Com pared to actin genes of animals, fungi, green plants and oomycetes, th at 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 in tron at the beginning of the coding region. The site of initiation of transcription was characterized by RNAse protection. The promoter regi on displays a CAAT box but lacks a canonical TATA motif. Other noticea ble 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 o bserved.