"Between DNA and proteins comes RNA, and an expanding realm of complexity," writes Heidi Ledford. "RNA is a shape-shifter, sometimes carrying genetic messages and sometimes regulating them, adopting a multitude of structures that can affect its function." Researchers are attempting to "define a second genetic code: one that predicts how segments of messenger RNA transcribed from a given gene can be mixed and matched to yield multiple products in different tissues, a process called alternative splicing."