While studying a mechanism of fibroin biosynthesis in the posterior silkgland of the silkworm larvae, an odd chromatographic interaction was observed between the silkgland RNA and a fibroin powder column. 1) A clear difference was found in respect of the elution pattern between RNAs prepared by a phenol method from the posterior gland of t h e normal larvae and of the genetic mutant incapable of synthesizing fibroin . 2) The difference disappeared when RNAs were chromatographed on a column of the methylated derivative instead of fibroin. 3) No marked difference could have been detected between the two RNAs with respect to the phosphorus-atomic absorption coefficient, ultracentrifugal behaviour and nucleotide composition. 4) RNA molecule of a higher mole cular weight and/or of a higher guanylic acid content is retained more firmly to fibroin. 5) K^+ ion is preferable to Na^+ ion in sharpening the chromatogram, and 10^-3 M Mg^++ ion dissociates the fibroin - RNA complex completely. In view of these results, it was suspected that a specific biological interaction in vivo between fibroin and a template RNA(s) in the field of the protein biosynthesis is revived at least in part in this mild gradient elution chromatography of the silkgland RNA on a fibroin powder column. It may thus provide in principle a unique method of isolating a proteinspecific RNA molecule (s), based on a molecular-biological specificity of its own.
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