Biochemical characterization of the yeast dynactin
complex. (A) Detergent solubility of Nip100-3xHA from whole-cell
extracts. Cells expressing Nip100-3xHA were lysed in buffer with or
without 0.2% Tween 20 nonionic detergent. The lysate was spun at
13,000 rpm in a microcentrifuge, and the low-speed supernatant was then
spun at 55,000 rpm (∼100,000 × g) in a tabletop
ultracentrifuge. Equal fractions of the whole-cell extract (W),
low-speed supernatant (LSS), low-speed pellet (LSP), high-speed
supernatant (HSS), and high-speed pellet (HSP) were analyzed by
immunoblotting with the 12CA5 anti-HA monoclonal
antibody. (B) Sucrose density gradient centrifugation indicates that
Nip100p, Act5p, and Jnm1p are all present in a 15.5S complex, which
does not include cytoplasmic dynein. High-speed supernatants from
wild-type or dyn1Δ strains expressing Nip100-3xHA were
analyzed in 7–18% sucrose gradients. Ten equal fractions were
collected and analyzed by SDS-PAGE and immunoblotting
using antibodies against the HA tag (wild-type panel, top row; and
dyn1Δ panel), Act5p (wild-type panel, second row), and Jnm1p
(wild-type panel, third row). Cross-reacting bands detected by the
antiAct5p antibody are denoted with an asterisk. Purified thyroglobulin
(19.4S), catalase (11.3S), and yeast alcohol dehydrogenase (7.4S) were
used as standards.