Assume you booked:

XX HNL-LAX
YY*/XX LAX-JFK
YY JFK-LHR
YY LHR-MIA
YY*/XX MIALAX
XX LAX-HNL

Here is what happens:

PNR Created by Priceline is the Booking Source PNR and will contain all segments. It will send booking messages to each carrier in the itinerary, both XX and YY in this example. XX and YY will both create a PNR. Generally, the booking messages will also contain all OA segments so they can be included in each carriers PNR for informational purposes -- faciliting through check-in, etc.

As the PNRs are created by XX and YY, their respective reservation system determines if any codeshare marketing segments are included. If so, it will then generate a booking message to the operating carrier to decrement inventory on the operating flight(s).

In this case, YY will send a booking message to XX for the two codeshare segments (LAX-JFK and MIA-LAX). XX will then create it's operating PNR to decrement inventory and for use during check-in, etc. These codeshare operating segments will almost always reside in a single PNR in the XX system. However, they will generally NOT appear in the XX PNR that was created from the original message from Priceline (although it actually depends on the functionality of the host reservation system and how the carrier has been configured within that system).