deleting spaces/merge question

Hello,

I have 4 columns of text imported from a txt file, so the cells appear as:

A B C D
1 1234 5613 1215 1541
2 5481 8913 1245 1521

What I would like to do is combine the information from a row of cells into a new cell. For example:

E
1 1234561312151541
2 5481891312451521

I can't seem to find a way to do it though. If I allow the cells to be imported as one cell (rather than 4) it inserts spaces between the groups of numbers, which I don't want.

Thanks, any help is appreciated.