Cover photograph (Copyright © 2000, American Society for Microbiology. All rights reserved.): Gal80p, the negative regulator of GAL gene expression in the yeast Saccharomyces cerevisiae, is a nucleocytoplasmic shuttling protein. Heterokaryons were formed between two kinds of yeast cells, one expressing Gal80p fused to green fluorescent protein, and the other expressing wild-type Gal80p. The Gal80p derivative distributes to both nuclei in the heterokaryon, indicating it has moved out of one nucleus and into the other through the shared cytoplasm. Cells and heterokaryons are viewed by Nomarski optics. (See related article in July 2000, issue 14: vol. 20, p. 5140.)