Simplify the following text for a Grade 9 native English-speaking person.
Original: He and others subsequently showed that the 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 .
Simplified: His group showed that cyclins bind and activate a family of protein kinases , now called the cyclin-dependent kinases . One of these had been identified as a crucial cell cycle regulator by Paul Nurse .