The temperature-dependent enzymatic breakdown of rRNA of reticulocytes.

The influence of temperature on the enzymatic breakdown of rRNA and ribosomal particles from rabbit reticulocytes by ribosomal ribonuclease and phosphatase was studied. Nucleosides were formed after the initial attack of ribonuclease on single-stranded regions of the RNA. The following conclusions were reached for free RNA: U and C were distributed in a random manner in the single-stranded loops at 20 °C. Short (A-U)-rich sequences were liberated at 37 °C, the relative share of which appeared to be higher in the 28-S RNA. It contained correspondingly longer G-C sequences. Clusters of A-U sequences of greater length than at 37 °C were melted at 50 °C. It was proved that only -U-U-U- sequences were split, by analysis of of the 3′ and 5′ terminal nucleotides of the primary split products of ribonuclease. The behaviour of the particle-bound RNA was modified considerably by interactions with proteins. Some of the cytosines appear to be protected against enzymatic attack at 20 °C. The 60-S subunit shows a strongly predominant melting of short U-A sequences at 37 °C. The reduction of the effective length of the U-A clusters may be due to interaction of the RNA with proteins. The 40-S subunit on the other hand would appear to exhibit a reduction of the effective length of G-C sequences. The interaction of the subunits with each other in an 80-S ribosome does not modify the behaviour of the subunits.