Using re to find only uppercase letters

[ranbarr]

Hi,
Im trying to solve a problem using re module, and one of the requests is to find a string with the letters ATGC only in uppercase.
this is my code:

def isVCF(file):
    num_format = re.compile(r"^chr(?:0?[1-9]|[1-9][0-9]|[MXY])\t0*[1-9][0-9]*\t[^\t]*(?:\t[ATCG]){2}\t")
    with open(file, "r+") as my_file:
        for line in my_file:
            if not num_format.match(line):
                return False
        return True

and this is an example to a line:

Output:
ChrX	74226540		T	t	50	.

The problem is that its matching the lowercase "t" aswell and I only want it to find uppercase letters.
I've tried several things but none worked.
Appreciate any kind of help!