INTERSPECIES CONSERVATION OF OUTER ARM DYNEIN INTERMEDIATE CHAIN SEQUENCES DEFINES 2 INTERMEDIATE CHAIN SUBCLASSES

Immunological analysis showed that antibodies against the intermediate chains (ICs) IC2 and IC3 of sea urchin outer arm dynein specifically cross-reacted with intermediate chains IC78 and IC69, respectively, of Chlamydomonas outer arm dynein. In contrast, no specific cross-reacti vity with any Chlamydomonas outer arm polypeptide was observed using a ntibody against IC1 of sea urchin outer arm dynein. To learn more abou t the relationships between the different ICs, overlapping cDNAs encod ing all of IC2 and IC3 of sea urchin were isolated and sequenced. Comp arison of these sequences with those previously obtained for the Chlam ydomonas ICs revealed that, although all four chains are homologous, s ea urchin IC2 is much more closely related to Chlamydomonas IC78 (45.8 % identity), and sea urchin IC3 is much more closely related to Chlamy domonas IC69 (48.5% identity), than either sea urchin chain is related to the other (23.5% identity). For homologous pairs, the similarities extend throughout the full lengths of the chains. Regions of similari ty between all four ICs and the IC (IC74) of cytoplasmic dynein, locat ed in the C-terminal halves of the chains, are due primarily to conser vation of the WD repeats present in all of these ICs. This is the firs t demonstration that structural differences between individual ICs wit hin an outer arm dynein have been highly conserved in the dyneins of d istantly related species. The results provide a basis for the subclass ification of these chains.