THE DYNEIN GENES OF PARAMECIUM-TETRAURELIA - THE STRUCTURE AND EXPRESSION OF THE CILIARY BETA-CHAINS AND CYTOPLASMIC HEAVY-CHAINS

The genes encoding two Paramecium dynein heavy chains, DHC-6 and DHC-8 , have been cloned and sequenced. Sequence-specific antibodies demonst rate that DHC-6 encodes ciliary outer arm beta-chain and DHC-8 encodes a cytoplasmic dynein heavy chain. Therefore, this study is the first opportunity to compare the primary structures and expression of two he avy chains representing the two functional classes of dynein expressed in the same cell. Deciliation of paramecia results in the accumulatio n of mRNA from DHC-6, but not DHC-8. Nuclear run-on transcription expe riments demonstrate that this increase in the steady state concentrati on of DHC-6 mRNA is a consequence of a rapid induction of transcriptio n in response to deciliation. This is the first demonstration that dyn ein, like other axonemal components, is transcriptionally regulated du ring reciliation. Analyses of the sequences of the two Paramecium dyne ins and the dynein heavy chains from other organisms indicate that the heavy chain can be divided into three regions: 1) the sequence of the central catalytic domain is conserved among all dyneins; 2) the tail domain sequence, consisting of the N-terminal 1200 residues, different iates between axonemal and cytoplasmic dyneins; and 3) the N-terminal 200 residues are the most divergent and appear to classify the isoform s. The organization of the heavy chain predicts that the variable tail domain may be sufficient to target the dynein to the appropriate plac e in the cell.