A specific sequence of 6 bp occurs randomly once every few thousand bases. Restriction enzymes are named for the bacteria that produce them. Ssp I comes from the bacteria Sp haerotilus species. I was the first restriction enzyme isolated from Providencia stuartii. And Hpa I was the first restriction enzyme isolated from Haemophilus parainfluenzae.
Chromosomes are huge molecules containing many genes.
Before restriction enzymes were discovered, scientists could not tell where on the chromosome a specific gene was located. And even if we could tell where the gene was located, there was no way to manipulate it. Restriction enzymes solved this problem. Every time the same piece of DNA is cut with a given enzyme, the same fragments are produced. This means we can more readily determine the location of a particular gene and we can more readily locate it in the same DNA fragment.