Reaction of HeLa cell methyl-labelled 28S ribosomal RNA with sodium bisulphite: a conformational probe for methylated sequences.

The reaction of 14C methyl-labelled HeLa cell 28 S ribosomal RNA with sodium bisulphite was studied. Using conditions under which 30% of the total cytidine residues were de-aminated to uridine, the reactivities of individual cytidine residues near particular methylation sites differed widely; some underwent almost quantitative reaction, some showed intermediate reactivity and others were almost inert. The possible value of this method as a conformational probe for ribosomal RNA is discussed.

Nucleated sites for the assembly of cytoplasmic microtubules in the ectodermal cells of blastulae of Arbacia punctulata.

In the ectodermal cells of sea urchin blastulae, the microtubules converge and appear to make contact with three distinct cytoplasmic foci or satellites associated with the basal body of the cilium. Beneath the nucleus, which lies in the apical end of the cell, the microtubules are aligned predominantly parallel to the cell's long axis and could thus make contact with the satellites as is directly suggested by observations on sections at or near the planes of the satellites. After the embryos are treated with low temperature (0 degrees C), the microtubules disassemble; however, the satellites can still be recognized.