The tRNA CCA-adding enzyme adds CCA stepwise to immature transfer RNA molecules untemplated, but with high specificity. We examined the oligomerization state of the enzyme from Sulfolobus shibatae and its binding to transfer RNA molecules, using various biophysical and biochemical methods including size exclusion chromatography, multi-angle laser light scattering, small-angle X-ray scattering, and gel electrophoresis band mobility shift assay. The 48 kDa monomer forms a stable salt-resistant dimer in solution. Further dimerization of the dimeric enzyme to form a tetramer is induced by the binding of two tRNA molecules. The formation of a tetramer with only two bound tRNA molecules leads us to suggest that one pair of active sites may be specific for adding two C bases, which results in scrunching of the primer strand. An adjacent second pair of active sites may be specific for adding A after addition of two C bases which makes the 3' terminus long enough to reach the second pair of active sites. (C) 2000 Academic Press.
Bibliographical noteFunding Information:
We thank Huiming Li for help in small-angle X-ray scattering experiments and Bill Elioson for help in multi-angle laser light-scattering experiments. We thank Dr Peiyong Shi, Dongxian Yue, Nancy Maizels and Alan Weiner for providing an overexpression clone and discussion. We thank Dr Alan Weiner and Kozo Tomita for commenting on the manuscript. This work was supported by a NIH grant GM-57510 (to T.A.S.).
- Gel electrophoresis band mobility shift assay
- Multi-angle laser light scattering
- RNA polymerase
- Small-angle X-ray scattering