General :: Awk / Grep Or Sed - Find And Replace Recursively From Files

I am new to linux as well as awk, grep or sed. I need a find and replace command single liner or script that loops trough input file (file1) and find the particular input in file2 and add "!" in front of the found string.

Example:
input file: file1
g+h=o+p
a+b=c+d
file2 (file that need to look for)
a+b=c+d1e105
x+y=z+s5e105
g+h=o+pabcdefg
t+r=w+qxvyderf

Output file (file3 should look like this)
!a+b=c+d1e105
x+y=z+s5e105
!g+h=o+pabcdefg
t+r=w+qxvyderf

I have tried many awk and sed method of find and replce but it did not work the way I wanted. This is mainly due to my lack of experience in awk and sed. The program should loop trough file1 and find in file2 and output in file3 for the 1st (g+h=o+p) set then repeat the same process again for set 2 (a+b=c+d).