TABLE 1.

Summary of experimental exchange studies

Protein	Source species	Methoda	Sitesb	Variants	Exchange effects assayed	Citation
LacI	Escherichia coli	Sup	328 (360)	4038	Operon repression,   in vivo	Markiewicz et al. (1994)
Lysozyme	Phage T4	Sup	155 (164)	1918	Plaque size, in vivo	Rennell et al. (1991)
Interleukin-3	Homo sapiens	Sat	103 (152)	754	Cell proliferation,   in vivo	Olins et al. (1995)
Barnase	E. coli	Sat	109 (110)	676	RNAse activity, in vivo	Axe et al. (1998)
β-Lactamase	Pseudomonas	Sat	27 (246)	513	Ampicillin resistance,   in vivo	Materon and Palzkill (2001)
RecA	E. coli	Sat	20 (323)	380	Plaque size, in vivo	Hortnagel et al. (1999)
Reverse transcriptase	HIV	Sat	109 (300)	366	RNA-dependent DNA   polymerase activity,   in vivo	Wrobel et al. (1998)
Protease	HIV	Sat	99 (99)	336	Protease activity,   in vivo	Loeb et al. (1989)
Protein V	Phage f1	Sat	86 (87)	313	Host inhibition,   in vivo	Zabin et al. (1991)
Nuclease	Staphylococcus	Scan	143 (149)	290	ΔΔG, in vitro	Green et al. (1992); Meeker et al. (1996); Shortle et al. (1990)
Growth hormone	H. sapiens	Scan	50 (191)	50	Dissociation constant,   in vitro	Cunningham and Wells (1989)
Insulin	H. sapiens	Scan	37 (51)	37	Receptor affinity,   in vitro	Kristensen et al. (1997)
Total			1266	9671

^aSup, nonsense suppression; sat, saturation mutagenesis; scan, alanine scanning (Ala and Gly scanning in the case of Nuclease).

^bAmino acid positions altered (in parentheses, total number of positions in the protein).