DNA and RNA content of Chironomus thummi polytene chromosomes determined by micro column gel filtration.

A new microtechnique was used to determine the nucleic acid content of Chironomus polytene chromosomes. The method based on UV-microspectrophotometric measurement of alkali digested chromosome samples before and after gel filtration through Sephadex microcolumns permits the simultaneous estimation of DNA as well as RNA amount of single chromosomes and nucleoli. The DNA and RNA content of C. thummi salivary gland chromosomes I-III carrying a large number of puffs (but no nucleoli or Balbiani rings) corresponds roughly to their relative lengths. Chromosomes of the most frequent polyteny level (class B; probably 8192 C) contain 418 (Chromosome I), 372 (II), and 307 times 10-12 g DNA (III) and 116, 120 and 69 times 10-12 g RNA, respectively. The 4th chromosome, which carries the nucleolus and two Balbiani rings, contains about 150 times 10-12 g DNA and 328 times 10-12 g RNA. As the result of one of the last replication steps both DNA and RNA content of chromosomes I-III becomes duplicated whereas nucleolar RNA content is increased to a smaller extent.