This paper deals with the main functions of Uyghur action nominals in {-(Ị)š} as compared to the less productive infinitive suffix {-mAK} as well as the participial subordinators {-GAn}+({-lỊK}) and {-(y)(ị)dịɣan}+({-lỊK}). Some types of complement clauses are discussed where these suffixes are used in complementary distribution. Uyghur {-(Ị)š} has two basic functions. First, it derives nouns from verbs. Secondly, it appears as a subordinator in different types of subordinate clauses. In complement clauses, it competes with the participle {-GAn}. The paper systematizes complement-taking predicates in Uyghur according to their choice of action nominal or participial suffixes. Case forms of action nominals in {-(I)š} are grammaticalized as converbs. In converb clauses, there can be a choice between {-GAn} and {-(Ị)š}. Moreover, the paper discusses what semantic and syntactic features Uyghur action nominals in {-(Ị)š} share with Turkish action nominals in {-mA} and how they differ from Turkish {-(y)Ịš}.