The Euglena paraflagellar rod: structure, relationship to other flagellar components and preliminary biochemical characterization.

Demembranated flagella from Euglena gracilis consisted of three distinct components: a 9 + 2 axoneme of microtubules, an extensive surface coating of long and short mastigonemes and a lattice-like axial fibre known as the paraflagellar rod. Negatively stained preparations of isolated paraflagellar rods showed the major structural unit to be a 22 nm filament oriented at approximately 45 degrees to the long axis of the rod in a 7-start left-handed helical arrangement. Attachment of the paraflagellar rod to the flagellar axoneme was via a series of goblet-shaped projections, which anchored the rod to a single outer doublet microtubule. Comparisons of axonemes from E. gracilis bearing the paraflagellar rod with those of Chlamydomonas reinhardtii, in which it is absent, by polyacrylamide gel electrophoresis revealed the presence of two prominent additional peptides with molecular weights of 80,000 and 69,000. Exposure of Euglena axonemes to trypsin selectively solubilized the paraflagellar rod and also removed both proteins, which were therefore tentatively identified as the major subunit proteins of the rod and designed PFR 1 and 2, respectively. In addition to these details of the structure and composition of the paraflagellar rod, the mode of attachment of the axoneme of both long and short mastigonemes was also identified.