Final answer:
The PIWI proteins that bind in the primary pathway are Piwi, Aubergine, and Argonaute.
Step-by-step explanation:
The PIWI proteins that bind in the primary pathway are all of the above: Piwi, Aubergine, and Argonaute. These proteins are part of the Argonaute protein family and play a crucial role in the regulation of gene expression through small RNA molecules. Piwi proteins are mainly found in germline cells, Aubergine proteins are involved in the piRNA pathway during early development, and Argonaute proteins are present in various tissues and have diverse roles in RNA interference.