Getting rid of spaces in txt file with nucleotide sequences

Hi everyone.
I'm new int this forum but i had a lot of information of RNA-seq experiments.
In one of them i have a file with non matched sequences in a .txt format.
But i have a problem: it doesn't hav the initial ">" and the sequences are in this format (examples):

I already add the > symbol with some awk script but i can't get rid of the space and separate the sequences from the blank spaces.

I need sometime like this:

I wish the community can help me.

Grettings.