RNA



An unexpected, conserved element of the U3 snoRNA is required for Mpp10p association


STEVEN  WORMSLEY a1a2, DMITRY A.  SAMARSKY a3, MAURILLE J.  FOURNIER a4 and SUSAN J.  BASERGA a1a5c1
a1 Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06520-8040, USA
a2 Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8040, USA
a3 Program in Molecular Medicine, University of Massachusetts Medical Center, Worcester, Massachusetts 01605, USA
a4 Departments of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01605, USA
a5 Department of Genetics, Yale University School of Medicine, New Haven, Connecticut 06520-8040, USA

Abstract

The U3 small nucleolar ribonucleoprotein (snoRNP) is composed of a small nucleolar RNA (snoRNA) and at least 10 proteins. The U3 snoRNA base pairs with the pre-rRNA to carry out the A0, A1, and A2 processing reactions that lead to the release of the 18S rRNA from the nascent pre-rRNA transcript. The yeast U3 snoRNA can be divided into a short 5′ domain (nt 1–39) and a larger 3′ domain (73 to the 3′ end) separated by a stretch of nucleotides called the hinge region (nt 40–72). The sequences required for pre-rRNA base pairing are found in the 5′ domain and hinge region whereas the 3′ domain is largely covered with proteins. Mpp10p, one of the protein components unique to the U3 snoRNP, plays a role in processing at the A1 and A2 sites. Because of its critical role in U3 snoRNP function, we determined which sequences in the U3 snoRNA are required for Mpp10p association. Unlike fibrillarin and all the previous U3 snoRNP components studied in this manner, sequences in the 3′ domain are not sufficient for Mpp10p association. Instead, a conserved sequence element in the U3 snoRNA hinge region is required, placing Mpp10p near the 5′ domain that carries out the pre-rRNA base-pairing interactions in the functional center of the U3 snoRNP.

(Received February 23 2001)
(Revised March 13 2001)
(Accepted March 22 2001)


Key Words: nucleolus; RNA processing; rRNA.

Correspondence:
c1 Reprint requests to: Susan J. Baserga, Department of Therapeutic Radiology, HRT 317, PO Box 208040, Yale School of Medicine, New Haven, Connecticut 06520-8040, USA; e-mail: susan.baserga@yale.edu.