MOLECULAR ANALYSIS OF A CYTOPLASMIC DYNEIN LIGHT INTERMEDIATE CHAIN REVEALS HOMOLOGY TO A FAMILY OF ATPASES

Cytoplasmic dynein is a multi-subunit complex involved in retrograde o rganelle transport and some aspects of mitosis. In previous work we ha ve cloned and sequenced cDNAs encoding the rat cytoplasmic dynein heav y and intermediate chains. Here we report the cloning of the remaining class of cytoplasmic dynein subunits, which we refer to as the light intermediate chains (LICs: 53-59 kDa), Four LIC electrophoretic bands were resolved in purified bovine cytoplasmic dynein preparations by on e-dimensional gel electrophoresis. These four bands were simplified to two bands (LIC53/55 and LIC57/59) by alkaline phosphatase treatment. N-terminal amino acid sequence was obtained from a total of II proteol ytic peptides generated from both LIC53/55 and LIC57/59. Overlapping c DNA clones encoding LIC53/55 were isolated by oligonucleotide screenin g using probes based on the LIC53/55 peptide sequence. The cDNA sequen ce contained a 497 codon open reading frame encoding a polypeptide wit h a molecular mass of similar to 55 kDa, Each of the LIC53/55 peptides was found within the deduced amino acid sequence, as well as four of the LIC57/59 peptides. Analysis of the LIC53/55 primary sequence revea led homology with the ABC transporter family of ATPases in the region surrounding the P-loop sequence element. Together these data identify the LICs as a novel family of dynein subunits with potential ATPase ac tivity. They also reveal that the complexity of the LICs is due to bot h post-translational modification and the existence of at least two LI C polypeptides for which we propose the names LIC-1a and LIC-2.