Speedy A, also known as SPDYA, SPDY1, Ringo3 or SPY1, is a 313 amino acid protein that localizes to the nucleus and belongs to the speedy/ringo family. Expressed at high levels in testis and at lower levels in brain, kidney, heart, bone marrow, colon, lung, liver spleen and placenta, Speedy A functions to regulate the G1/S phase transition of the cell cycle, specifically by binding to and activating Cdc2 p34, Cdk2 and p27. Additionally, Speedy A mediates cell survival during DNA damage, suggesting that Speedy A plays a role in proper cell cycle progression throughout the life of the cell. Multiple isoforms of Speedy A exist due to alternative splicing events. The gene encoding Speedy A maps to human chromosome 2, which encodes over 1,400 genes and comprises nearly 8% of the human genome.