The Use of Iodinated RNA for Gene Localization

Carrier-free iodination of 5S RNA with125I yields a probe suitable for use in cytological RNA-DNA hybridization studies. The genes coding for 5S ribosomal RNA in Drosophila could be localized by autoradiography after a 2-day exposure, whereas a 2-month exposure is needed when the best available [3H]RNA is used. The procedure introduces one covalently bound125I atom per 100 nucleotides, resulting in a specific activity of over 108dpm/μ g of RNA. The method may be readily applied to other problems involving molecular hybridization techniques.