4897
To explore the mechanism of RSK activation , a cloned human RSK cDNA ( RSK3 ) was used to generate and characterize several site - directed RSK mutants ; K91A ( N - Lys , NH2 - terminal ATP - binding mutant ) , K444A ( C - Lys , COOH - terminal ATP - binding mutant ) , N / C - Lys ( double ATP - binding mutant ) T570A ( C - Thr , mutant of the putative MAPK phosphorylation site in subdomain VIII of the C - domain ) , S218A ( N - Ser , mutant of the corresponding NH2 - terminal residue ) .
 RSK, RSK, RSK3, RSK mutants, MAPK
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 RSK, RSK, RSK3, RSK mutants, MAPK