A subordinating conjuction is a conjuction that introduces a subordinate clause. A subordinating conjuction does two things in a sentence.
It illustrates the importance of the independent clause.
It provides a transition between two different parts of the sentence.
In the sentence, "Neither recordings nor photographs can be copied or borrowed because they are so fragile," because is the subordinating conjuction. It seperates the independent clause (Neither recordings nor photographs can be copied or borrowed) from the subordinate clause (they are so fragile).
