Sublime

abbreviated RNAase or RNase,

The three-dimensional structure of the Tetrahymena self-splicing RNA was modeled by François Michel and Eric Westhof. The intron (light-shaded) pairs with the RNA near the site of splicing (dark-shaded). The intron also binds a molecule of guanosine (G), itself one of the building blocks of RNA, and uses it as chemical scissors to cleave the black

that chopped long double-stranded RNA into smaller pieces called small interfering RNAs (siRNAs).

there were six varieties, and because they were rich in uracil (the letter U in the RNA alphabet), they had been dubbed U1 through U6.

These were then bound and shepherded to their sites of action by another enzyme researchers dubbed Argonaute,

U6 enters the scene tightly entwined with U4, and together they find their place on the intron. But then U2 butts in, stealing away U6, and U4 exits the stage in a huff. Now U6 and U2, with some help from U5, are free to produce the chemistry needed to complete the splicing reaction. Together they act as a ribozyme, catalyzing the mRNA splicing pro

The CRISPR-Cas9 bacterial defense complex (left) has a guide RNA that recognizes a target phage DNA sequence and a tracrRNA that base-pairs with the guide RNA and holds on to the Cas9 protein. Cas9 then cleaves both strands of the DNA. An engineered form of CRISPR-Cas9 used for genome editing (right) has the two natural RNAs fused to form a single-

indicating that an amino acid had been joined to an RNA. Such a linkage had never been observed before, but it was exactly what would happen if there was an RNA whose job it was to adapt RNA codons to amino acids. Later these small RNAs became known as transfer RNAs (tRNAs), because they transfer the correct amino acid to the growing protein chain