When you play or scrub through a sequence that contains a clip based on a movie from a Nikon D7000 camera, playback is not smooth.
Adobe Premiere Pro can natively decode some movies wrapped in QuickTime containers, without using QuickTime Player. Native decoding is much faster than going through the QuickTime component.
When Adobe Premiere Pro imports .mov files from a Nikon D7000 camera, it mistakenly thinks that it must use the QuickTime component for reading the file. By changing the filename extension to .mpg, you are telling Adobe Premiere Pro to use its native MPEG decoding component, which is much faster.
If this solution doesn't work for you, come to the Adobe Premiere Pro user-to-user forum for assistance.