He and others subsequently showed that cyclins bind and activate a family of protein kinases, now called the cyclin-dependent kinases, one of which had been identified as a crucial cell cycle regulator by Paul Nurse.
Ia dan mitranya kemudian menunjukkan bahwa siklin berikatan dan mengaktifkan segolongan protein kinase, kini disebut kinase bergantung protein, salah satu darinya telah dikenali sebagai pengatur siklus sel penting oleh Paul Maxime Nurse.