Polymorphism of Serine Specific Transfer Ribonucleic Acid

A method is described for the crystallizatino of serine specific transfer ribonucleic acid (tRNAI+IISer) in the prsence of magnesium as a divalent counter ion. The crystallization conditions in relation to different temperatures and various tRNA concentrations were investigated in detail were and three crystal forms were found. Tentative values for the unit cell parameters for two forms determined from X‐ray powder photographs. For the first form a= 120.3 Å, b= 54.2 Å and c= 68.6 Å and the space group is probably P222; for the second form a= 213.2 Å and c= 115.7 Å and the space group is either P6 or P622. From the thrid crystal form a still X‐ray photograph with reflections out to 3.5 Å from a single crystal was obtained using a precession camera. This phtograph together with a precession photograph suggests monolinic symmetry with the cell dimensions of a= 63 Å, b= 41 Å, c= 112 Å and β= 102.30, with the possible space group P21.