No abstract

Seven L-arabinose-negative mutations are described that map in three genetically distinct regions immediately adjacent to the araO (operator) region of the L-arabinose operon. All seven mutants revert spontaneously, exhibit a cis-dominant, trans-recessive polarity effect upon the expression of L-arabinose isomerase (gene araA), and fail to respond to amber, ochre, or UGA suppressors. Three of these mutants exhibit absolute polarity and are not reverted by the mutangens 2-aminopurine, diethyl sulfate, and ICR-191. These may have arisen as a consequence of an insertion mutation in gene araB or in the initiator region of the L-arabinose operon. The four remaining mutants exhibit strong but not absolute polarity on gene araA and respond to the mutagens diethyl sulfate and ICR-191. Three of these mutants are suppressible by two independently isolated suppressors that fail to suppress known nonsense codons. Partially polar Ara+ revertants with lesions linked to ara are obtained from three of the same four mutants. These polar mutants, their external suppressors, and their partially polar revertants are discussed in terms of the mechanism of initiation of expression of the L-arabinose operon. 383on July 31, 2020 by guest

No abstract

Tbe fruit of the coffee plant {Coffea arabica) was analyzed for auxin protector content. Ripe coffee berries were separated into pit and pulp, ground in buffer, and assayed for auxin protectors. The extracts were then subjected to gel filtration in order to determine tbe molecular weight of the protector(s).