The nonprime sector provided a lot of the muscle for the mortgage market in the early part of 2006, but there are signs that the sector may be feeling some strain. Inside Mortgage Finance estimates that $237 billion in new subprime and Alternative A loans were originated during the first quarter of 2006. That meant nonprime loans accounted for a huge 34.9 percent of the total $680 billion in total first-quarter mortgage originations. … [One data table included]