title: Corrections and clarifications.
abstract: In the report "A three-dimensional model for the hammerhead ribozyme based on fluorescence measurements" by T. Tuschl et al. (4 Nov. 1994, p. 785), the text of lines 28 through 30 in column 3 on page 785 should have read, "... we located 5-carboxyfluorescein at (d, -29.5 degrees , L-3.75 A) and 5-carboxytetramethylrhodamine at (a, -29.5 degrees -delta, -3.75 A)." In the same report, the second line of equation 1 in the legend to figure 3 was incorrectly printed. The correct equation appears below. [See the equation in the PDF file] Equation 1 in note 17 of the same report was also incorrectly printed. The correct equation appears below. [see the equation in the PDF file].