CSHL team traces extensive networks regulating alternative RN...(lative size of other genomes that surpri...)

The common fruit fly that hovers over your ripening bananas, for instance, possesses some 14,000 genes. It's perfectly obvious that human beings are vastly more complex, biologically, than a fly. Molecular biologists have demonstrated in recent years that it is not the number of genes that is the key to complexity but rather the number and diversity of gene products that a given set of genes can instruct cells to manufacture.

Rather than a single gene ordering the production of a single kind of protein, as scientists used to assume, it turns out that individual genes can in some cases give rise to dozens or even thousands of different proteins, thanks to a phenomenon called alternative splicing.

Zhang and Krainer's new research focused on splicing, which is the "editing" of RNA molecules generated by activated genes. By cutting up and pasting back together bits of these RNA intermediaries, the splicing machinery deletes "non-coding" segments (called introns) and stitches together "coding" segments (called exons).

The final product of RNA splicing (called a mature messenger-RNA "transcript") finds its way out of the cell nucleus. Carrying the "message" of an activated gene, it enters a structure called the ribosome, which reads its coding instructions and manufactures a protein with a particular configuration. The protein's shape--and function--will vary depending on how the splicing factors back in the nucleus have cut and pasted together the final RNA transcript which has served as the blueprint for the protein's manufacture.

The question addressed by Zhang and Krainer is how particular splicing factors can recognize their specific targets. How do these proteins know where to attach to raw, "unedited" RNA transcripts, and how do they engage the cellular machinery that actually splices RNAs--a compl
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