| Autor: |
Hannon, G J, Maroney, P A, Branch, A, Benenfield, B J, Robertson, H D, Nilsen, T W |
| Zdroj: |
Molecular and Cellular Biology; October 1989, Vol. 9 Issue: 10 p4422-4431, 10p |
| Abstrakt: |
We report here that the mature 5' terminus of human 18S rRNA is generated in vitro by a two-step processing reaction. In the first step, SP6 transcripts were specifically cleaved in HeLa cell nucleolar extract at three positions near the external transcribed spacer (ETS)-18S boundary. Of these cleavage sites, two were major and the other was minor. RNase T1 fingerprint and secondary nuclease analyses placed the two major cleavage sites 3 and 8 bases upstream from the mature 5' end of 18S rRNA and the minor cleavage site 1 base into the 18S sequence. All three cleavages yielded 5'-hydroxyl, 2'-3'-cyclic phosphate termini and were 5' of adenosine residues in the sequence UACCU, which was repeated three times near the ETS-18S boundary. In the second step, the initial cleavage product containing 3 bases of ETS was converted to an RNA with a 5' terminus identical to that of mature 18S RNA by an activity found in HeLa cell cytoplasmic extracts. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
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