Domains in the 1α dynein heavy chain required for inner arm assembly and flagellar motility in Chlamydomonas

Flagellar motility is generated by the activity of multiple dynein motors, but the specific role of each dynein heavy chain (Dhc) is largely unknown, and the mechanism by which the different Dhcs are targeted to their unique locations is also poorly understood. We report here the complete nucleotide sequence of the Chlamydomonas Dhc1 gene and the corresponding deduced amino acid sequence of the 1 alpha Dhc of the I1 inner dynein arm. The la Dhe is similar to other axonemal Dhcs, but two additional phosphate binding motifs (P-loops) have been identified in the NH2- and COOH-terminal regions. Because mutations in Dhc1 result in motility defects and loss of the I1 inner arm, a series of Dhc1 transgenes were used to rescue the mutant phenotypes. Motile cotransformants that express either full-length or truncated 1 alpha Dhcs were recovered. The truncated 1 alpha Dhc fragments lacked the dynein motor domain, but still assembled with the I beta Dhc and other I1 subunits into partially functional complexes at the correct axoneme location. Analysis of the transformants has identified the site of the 1 alpha motor domain in the I1 structure and further revealed the role of the 1 alpha Dhc in flagellar motility and phototactic behavior.