Initially the only way of identifying tRNA genes was by DNA-RNA hy­ bridization. The discovery that informational suppression may result from muta­ tions in tRNA genes has not only allowed their genetic analysis but has led to the isolation of mutants important in understanding the function, structure, and synthesis of tRNA. Genetic analysis has also established the role of tRNA in the regulation of at least one biosynthetic pathway. Earlier work on informational suppression has been reviewed in a classical article by Gorini (1). Other aspects of transfer RNA recently reviewed are: tRNA structure (2, 3); tRNA recognition by aminoacyl tRNA synthetase (4, 5); function and synthesis of modified bases in tRNA (6). A useful and exhaustive compilation of references to tRNA re­ search has also been published (7).