Nuclear travel costs energy

The nucleus is a crowded place, with chromatin, nuclear speckles, and nucleoli clogging up the works. Although the usual crop of molecular motors have not been found in the nucleus, many nuclear molecules are able to move from place to place. Recently, diffusion has been argued to be the principal means of nuclear travel. But new results from Calapez et al. (page 795) argue that Brownian motion does not account for everything. Something is using energy to help large particles move in the nucleus.

Large particles that must traverse the nucleus include mRNPs, a complex of mRNA and several associated protein factors. Calapez et al. analyzed mRNP movement from chromatin to the nuclear pore by FRAP analysis of two mRNA-binding proteins tagged with GFP. mRNP complexes moved more quickly than dextrans of...