It's fine the way it is. Structure is the key.
ascribe is a double object verb: it takes a direct object and an indirect object, and you can switch them around, like this,
 They ascribe to the conjunction the meaning of . . . .
 They ascribe the meaning of . . . to the conjunction.
Note,  and  are in active voice. In passive voice, the direct object takes over the structural subject position,
 The meaning of . . . is ascribed to the conjunction.
 To the conjunction, the meaning of . . . is ascribed.
In , the indirect object is topicalized, or moved to the front for emphasis.
Now, in our examples below, 'be ascribed' looks a lot like passive voice:
 . . . genes, of which 36% can be ascribed (by us to have) a putative function.
Here's the same sentence, without the 'of which' phrase,
 36% of the genes can be ascribed (by us to have) a putative function.
Active voice yields  and ,
 We ascribe a putative function to 36% of the genes.
 We ascribe to 36% of the genes a putative function.
Look! In , there's the missing 'to' you've been looking for.
All the best,