22862
Data on base excision repair ( BER ) , direct reversal with O ( 6 ) - alkylguanine transferase and double strand breaks repair , although rather scarce , are being reviewed , as well as nucleotide excision repair ( NER ) and photoreactivation repair ( PER ) , which are by far the most studied repair mechanisms in fish .
 Chemical: O ( 6 ) - alkylguanine; Chemical: nucleotide
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: O ( 6 ) - alkylguanine; Chemical: nucleotide