All the UC medical schools have a PRIME (Program in Medical Education) program whose goal is to develop doctors for underserved communities. Each PRIME program has a different focus, they include: rural, inner city, health equity, San Joaquin Valley, latino community; I think UCLA PRIME really focuses in in the leadership component in developing physician-leaders for underserved.
CDU/UCLA (24 students?) is partnership between the two institutions, whose goal is also to develop physicians for underserved communities. This is a great programs as you have the resources of 2 schools, more financial aid?, more administrative personal to support you. UCLA PRIME (18 students) is a 5 year program requires a student to earn a Masters degree (I'm not sure if its still funded), CDU/UCLA is a 4 year program and I believe students are required to develop a research thesis. I believe Clinical rotations for both these programs tend to be in underserved areas (as compared to regular UCLA SOM where rotations not required to be in underserved sites)
You apply to the 3 programs separately as they each have their own admissions committee.