Table 1.

Conformational changes observed in the four structures and related crystal structures (see ref. 8)

	Rotation angle (°)	L1 stalk movement		Distance between the tRNAs (Å)	Distance between L1 and the tRNA (Å)
		Inward rotation (°)	Forward rotation (°)
2I2U-2I2V	0	0	0
NR	1.0	7	−10	41	93
IRS1	3.2	12	−10	59	69
IRS2	4.9	21	−5	66	60
RS	7.5	35	12	69	37
3I1O -3I1P	0.8	1	−9	N/A
3I1M -3I1N	6.3	−4	2
3I1S -3I1T	−0.9	3	−3
3I1Q -3I1R	5.0	0	0
3I21 -3I22	−0.6	3	−5
3I1Z -3I20	5.1	0	0

“Rotation angle” refers to the counterclockwise rotation of the 30S subunit with respect to the 50S subunit, viewed from the 30S subunit’s solvent side. “Larger angle” means larger degree of rotation. The “inward rotation” refers to the inward movement of the L1 stalk toward the main body of the ribosome. The “forward rotation” refers to the movement of the L1 stalk toward the 30S subunit of the ribosome. “Distance between tRNAs” refers to the distance between residue 47 of the A-site tRNA and residue 8 of the P-site tRNA, measured based on atomic models obtained trough real-space refinement. “Distance between L1 and the P-site tRNA” refers to the distance between residue 55 of the L1 stalk protein and residue 8 of the P-site tRNA. The model of the L1 stalk protein was obtained by aligning the L1 stalk of 3KNI, which contains the L1 stalk protein, with the atomic models of L1 stalk base obtained by real-space refinement.