Published online 27 February 2004
Nucleic Acids Research, 2004, Vol. 32, No. 4 1404-1413
© 2004 Oxford University Press
Two-hybrid Mpp10p interaction-defective Imp4 proteins are not interaction defective in vivo but do confer specific pre-rRNA processing defects in Saccharomyces cerevisiae
1 Department of Genetics, 2 Department of Molecular Biophysics and Biochemistry and 3 Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520-8024, USA
*To whom correspondence should be addressed at Yale University School of Medicine, Department of Molecular Biophysics and Biochemistry, 333 Cedar Street, PO Box 208024, New Haven, CT 06530-8024, USA. Tel: +1 203 785 4618; Fax: +1 203 785 6404; Email: susan.baserga{at}yale.edu
The SSU processome is a large, evolutionarily conserved ribonucleoprotein (RNP), consisting of the U3 snoRNA and at least 28 protein components, that is required for biogenesis of the 18S rRNA. We tested the function of one proteinprotein interaction in the SSU processome, Mpp10pImp4p, in ribosome biogenesis. Exploiting the reverse two-hybrid system, we screened for mutated Imp4 proteins that were conditionally defective for interaction with Mpp10p. Three different imp4 sequences were isolated that: (i) conferred conditional growth in the two-hybrid strain; (ii) complemented the disrupted imp4; (iii) conferred conditional growth in the context of their normal cellular function; and (iv) resulted in defective pre-rRNA processing at the non-permissive temperatures. Domain swapping revealed that mutations that conferred cold sensitivity resided in the N-terminal coiled-coil domain while mutations in the C-terminus conferred temperature sensitivity. Surprisingly, the mutated Imp4 proteins were not measurably defective for interaction with Mpp10p in the context of the SSU processome. This suggests that other members of the complex may contribute to maintaining the Mpp10pImp4p interaction in this large RNP. Since proteinprotein interactions are critical for many different aspects of cellular metabolism, our work has implications for the study of other large protein complexes.
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