STRUCTURAL BASIS FOR THE CATALYTIC MECHANISM AND SUBSTRATE-SPECIFICITY OF THE RIBONUCLEASE ALPHA-SARCIN

alpha-Sarcin is a ribosome-inactivating protein which selectively clea ves a single phosphodiester bond in a universally conserved sequence o f the major rRNA. The solution structure of alpha-sarcin has been dete rmined on the basis of 1898 distance and angular experimental constrai nts from NMR spectroscopy. It reveals a catalytic mechanism analogous to that of the T-1 family of ribonucleases while its exquisite specifi city resides in the contacts provided by its distinctive loops.