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J. Biol. Chem., Vol. 281, Issue 41, 31050-31060, October 13, 2006

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The Unorthodox SNAP50 Zinc Finger Domain Contributes to Cooperative Promoter Recognition by Human SNAP_C^*

Gauri W. Jawdekar, Andrej Hanzlowsky, Stacy L. Hovde, Blanka Jelencic, Michael Feig^¶, James H. Geiger¹, and R. William Henry^¶2

From the Departments ofMicrobiology & Molecular Genetics, Chemistry, and ^¶Biochemistry & Molecular Biology, Michigan State University, East Lansing, Michigan 48824

Human small nuclear RNA gene transcription by RNA polymerases II and III depends upon promoter recognition by the SNAP_C general transcription factor. DNA binding by SNAP_C involves direct DNA contacts by the SNAP190 subunit in cooperation with SNAP50 and SNAP43. The data presented herein shows that SNAP50 plays an important role in DNA binding by SNAP_C through its zinc finger domain. The SNAP50 zinc finger domain contains 15 cysteine and histidine residues configured in two potential zinc coordination arrangements. Individual alanine substitution of each cysteine and histidine residue demonstrated that eight sites are important for DNA binding by SNAP_C. However, metal binding studies revealed that SNAP_C contains a single zinc atom indicating that only one coordination site functions as a zinc finger. Of the eight residues critical for DNA binding, four cysteine residues were also essential for both U1 and U6 transcription by RNA polymerase II and III, respectively. Surprisingly, the remaining four residues, although critical for U1 transcription could support partial U6 transcription. DNA binding studies showed that defects in DNA binding by SNAP_C alone could be suppressed through cooperative DNA binding with another member of the RNA polymerase III general transcription machinery, TFIIIB. These results suggest that these eight cysteine and histidine residues perform different functions during DNA binding with those residues involved in zinc coordination likely performing a dominant role in domain stabilization and the others involved in DNA binding. These data further define the unorthodox SNAP50 zinc finger region as an evolutionarily conserved DNA binding domain.

Received for publication, April 20, 2006 , and in revised form, July 5, 2006.

^* This work was supported by National Institutes of Health Grants R01-GM59805 (to R. W. H.) and R01-GM063894 (to J. H. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence may be addressed. Tel.: 517-355-9715 (ext. 234).

² To whom correspondence may be addressed. Tel.: 517-353-3980; Fax: 517-353-9334; E-mail: henryrw{at}msu.edu.

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