BEAT FREQUENCY DIFFERENCE BETWEEN THE 2 FLAGELLA OF CHLAMYDOMONAS DEPENDS ON THE ATTACHMENT SITE OF OUTER DYNEIN ARMS ON THE OUTER-DOUBLER MICROTUBULES

The two flagella of Chlamydomonas, although similar to each other at f irst glance, differ in functional properties. A clear difference exist s in the beat frequency: the trans-flagellum (the one farthest from th e eyespot) beats with 30-40% higher frequency than the cis-flagellum ( the one nearest to the eyespot) in demembranated and reactivated cell models. This difference is considered to be influenced by outer arm dy nein, because the two flagella beat at almost the same frequency in ce ll models of oda mutants lacking the outer dynein arm. When a sample o f outer arm dynein extracted and purified from the wild-type axoneme w as mixed with the cell models of an oda mutant, odal, an almost normal number of outer dynein arms became attached to the axonemes, and the wild-type level of beat frequency was recovered on reactivation with A TP addition. The frequency imbalance, however, was not restored. Unexp ectedly, when a similar experiment was performed with the cell model o f another oda mutant, oda6, the addition of outer arm dynein restored the cis-trans frequency imbalance in addition to the normal number of outer arms and the higher level of reactivated motility. Among other o da mutants, oda3 yielded results similar to those with odal, whereas o da2, oda4, and oda5 yielded results similar to those with oda6. Becaus e the only structural difference between the two groups of oda mutants is that the odal and oda3 axonemes lack the outer arm attachment site on the outer doublet A-tubule while the axonemes of the other mutants retain it, these findings suggest that the attachment site for the ou ter dynein arm is important in determining the flagellar beat frequenc y. This suggests that the basal portion of the outer arm dynein is imp ortant in regulating the flagellar activity and therefore the behavior of the cell. (C) 1997 Wiley-Liss, Inc.