In vitro iodination of plant ribonucleic acids

The optimum conditions for in vitro iodination of RNAs have been established which yield specific radioactivities ranging from 10 × 104 to 10 × 106 cpm/μg. A nomogram has been constructed by correlating specific radioactivities of RNA with concentration of KI, RNA, and 125I. This nomogram can be used to determine the conditions for the desired specific radioactivities for any unknown RNA. The in vitro iodinated RNA has been compared with in vivo labeled RNA for hybridization characteristics. Competition hybridization between 125I-labeled chloroplast-rRNA and unlabeled pea (Pisum sativum) chloroplast-rRNA was identical to that found using [32P]chloroplast-rRNA. Thermal stability of $\text{DNA-}^{125}\text{I-rRNA}$ hybrids was similar to the thermal stability of $\text{DNA-}[^{32}\text{P}]\text{rRNA}$ hybrids. The iodinated RNA was not found to have undergone any changes in its hydrogen-bonding properties.