realized in primer role (cell and molecular biology) A short strand of RNA that is synthesized along single-stranded DNA during replication, initiating DNA polymerase-catalyzed synthesis of the complementary strand. http://www.answers.com/topic/rna-primer primer role a complementary nucleotide probe role which inheres in nucleic acid molecular entity and is realized by the use of the entity bearing the role to initiate chain elongation. polymerase chain reaction complementary nucleotide probe role