A comparison of the solution structures and conformational properties of the somatic and oocyte 5S rRNAs of XXXX .

@entity1238 @entity1133 @entity6546 @entity4338 @entity8723 @entity377 @entity1098
The secondary and tertiary structures of @entity1238 oocyte and somatic 5S rRNAs were investigated using chemical and enzymatic probes. The accessibility of both RNAs towards single-strand specific nucleases (T1, T2, A and S1) and a helix-specific ribonuclease from cobra venom (RNase V1) was determined. The reactivity of nucleobase N7, N3 and N1 positions towards chemical probes was investigated under native (5 mM @entity8723 , 100 mM @entity4338 , 20 degrees C) and semi-denaturing (1 mM @entity1098 , 20 degrees C) conditions. Ethylnitrosourea was used to identify @entity6546 not reactive towards alkylation under native conditions. The results obtained confirm the presence of the five helical stems predicted by the consensus secondary structure model of 5S rRNA. The chemical reactivity data indicate that loops C and D are involved in a number of tertiary interactions, and loop E folds into an unusual secondary structure. A comparison of the data obtained for the two types of @entity1238 5S rRNA indicates that the conformations of the oocyte and somatic 5S rRNAs are very similar. However, the data obtained with nucleases under native conditions, and chemical probes under semi-denaturing conditions, reveal that helices III and IV in the somatic 5S rRNA are less stable than the same structures in oocyte 5S rRNA. Using chimeric 5S rRNAs, it was possible to demonstrate that the relative resistance of oocyte 5S rRNA to partial denaturation in 4 M @entity1133 is conferred by the five oocyte-specific @entity377 substitutions in loop B/helix III. In contrast, the superior stability of oocyte 5S rRNA in the presence of @entity1098 is related to a single C substitution at position 79.
