How to grep until a certain character?

Hi, so I have a file containing many repetitions of the pattern block displayed below:

I was wondering how to grep, for example, a block starting with the line containing "NM_13489075" and everything else after it until the line with ">NM_#######". So I want to grep:

I'm doing this for the purpose of replacing the first line with something else, but keeping the rest intact and right under it to be echoed later.

Thanks for any help!